As it is now well known, I2a1 is a typical European haplogroup. It is present all over the continent with maximum frequencies recorded in Bosnia (particularly among Bosnian Croats), Sardinia, Croatia, Serbia (+30%), Montenegro, Romania, Moldova, Bulgaria, and Macedonia (+20%). The percentages of I2a1a2b-L621 clade in Slovenia, Ukraine, and Russia available on the Internet should be taken with caution because they are definitely smaller: up to 13% in Slovenia, 16% in Ukraine, and about 7-8% in Russia. (According to the study of Andrej Zupan /2014/, and data from Ukrainian and Russian DNA projects /2020/)
Haplogroup I2a1a2b-L621, or to be precise, its subclade Y3120, is often considered as another “Slavic” haplogroup (beside R1a-Z282), which is wrong and scientifically inadmissible. The criterion of coherence is unambiguous: “Individuals from genetically distinguishable groups should not be given the same name; individuals from genetically indistinguishable ones should.”
Haplogroups are a genetic, and not a geographical, linguistic, national, or social category. This means that they cannot be designated according to the language their carriers speak, the country they live in, or religion they practice... Each haplogroup denotes a common genetic origin of the people who share it, and they all belong to the same ethno-racial group which has had its own evolution.
In some cases, haplogroups are easily associated with certain ethno-racial/genetic groups.
For example, it is obvious that most of today’s European R1a people are the Slavs, the R1b people are the Celts (or, to be precise: not all R1b men are the Celts, but all Celts are R1b!!), and I1a people are the “Northmen” or Germans in general. Of course, the ancestors of these people were not known by those names 3000 years ago, but they, nevertheless, inherited the same Y-DNA lineages which genetic or ethno-racial Slavs, Celts, and Northmen/Germans inherit today.
Apparently, Y-chromosome studies discovered (and proved) that Slavs and Germans are not just “ethno-linguistic” but also indisputable “ethno-racial” categories – groups of men sharing the same paternal lineages or ancestors. And, for that reason it is necessary to distinguish “I1a Germans” and “R1a Slavs” from the national Germans/Deutsche, Danes, Russians, Poles… (carriers of other haplogroups) who are “Germans” or “Slavs” according to the language they speak (ethno-linguistic) but not according to origin.
Unfortunately, even though the haplogroup I2a is believed to have been one of the haplogroups of the first anatomically modern humans to inhabit Europe, Cro-Magnons, there is no single common name for all I2a people now. Nevertheless, “I2a1 people” still represent a separate, distinct ethno-racial group, and they have always been (and will be) I2a1 people, regardless of the subclade, or nation they belong to, time flow, migrations of their ancestors, place they live in, or the language they speak. And, the most appropriate name for the haplogroup we are talking about is Dinaric-Carpathian – without any national connotations.
Nations are mixtures of different haplogroups, but haplogroups themselves do not mix – they are inherited linearly: from father to son. Therefore, not a single I2a1a2b man participated in the ethnogenesis of the genetic/ethno-racial Slavs, but many I2a1a2b people definitely participated in the ethnogenesis of Slavic (or Germanic, Romance…) speaking nations.
 Eisenmann, S., Bánffy, E., van Dommelen, P. et al. Reconciling material cultures in archaeology with genetic data: The nomenclature of clusters emerging from archaeogenomic analysis. Sci Rep 8, 13003 (2018). https://doi.org/10.1038/s41598-018-31123-z
 Jones, Eppie R et al. “Upper Palaeolithic genomes reveal deep roots of modern Eurasians.” Nature communications vol. 6 8912. 16 Nov. 2015, doi:10.1038/ncomms9912
According to data collected from an extensive research that has been conducted in the last dozen years, and thousands of ancient and modern DNA test results from different European countries, it seems that the haplogroup I2a-L621 appeared somewhere along the Lower Danube about 12.000 ybp. There is also archeogenetic evidence that some I2a-L621 people lived in the area of today’s Bulgaria 5000 years ago. (ReichLab 2020. SE_Europe; https://haplogroup.info/all-ancient-dna.pdf ) However, the carriers of its oldest lineages have managed to survive until today in central-western Europe. (https://www.yfull.com/tree/I-L621/) No one can tell how or when they arrived in the area, or even if the haplogroup Y3120 (formed 3800 ybp) appeared there or not. At present, it is only confirmed that the “Y3120* men”, negative for downstream branches, live in the Balkans (9 different surnames from Serbia, Bosnia and Herzegovina, Croatia https://dnk.poreklo.rs/DNK-projekat/ ). And, there are some Montenegrins who are yet to be verified.
The initial lack of knowledge and information was confusing and it produced (not less than) two contradicted theories about the place of origin of I-Y3120 and, particularly, its subclades Y4460, Y18331, S17250, and Z17855 which were all formed ~2100 years ago:
The debate was mostly futile, and many arguments and premises proved to be insignificant, or simply wrong. Namely, the attention was focused on the issues such as haplogroup frequency, the number of representatives, haplotype diversity, archaeological learning of the distant past…, but it turned out that these parameters were unreliable “tools” in locating the area where Y3120 subclades originated, and they were of little help in explaining their development. However, in the last few years, thanks to BigY and SNP test results, the fog has cleared, and it became evident that genetics and history complemented each other.
The first thing that catches the eye of an interested person is the “I2a1 map” provided above. It unmistakably shows that the south-eastern Europe is the “source” of expansion of haplogroup I2a1 (Y3120), but it is not explicit whether it is the eastern or western Balkans. Still, the overall research and some important recent findings go in favour of the eastern side of the peninsula and the Romanian section of the Carpathian Mountains.
Here are some raw facts:
- The carriers of Y3120 subclades live all over south-eastern and north-eastern/north-western Europe. The number of I2a1 people is greater in the north than in the south. But the south-eastern Europe (from Croatia to Greece and Bulgaria) is the only region where all I-Y3120 subclades are clustered together. It is even more significant that the basal lineages of all Y3120 subclades are found exclusively in the Balkans (and Hungary). (see https://www.yfull.com/tree/I-Y3120/, and Y4460 results at https://bosnjackidnk.com/)The subgroups Y18331, S17250-PH908, and Z17855 are also present in the same area with younger branches and many offsprings – it undoubtedly points to a spatial and temporal continuity of some 2100-2300 years.
Annotation: The larger I2a1 population and the “exclusive” variety of Y4460, S17250-Y4882 and S17250-Y5596 subclades in the “upper” Europe are the consequences of (frequent) migrations over the course of more than 1500 years and, above all, the development of younger branches.
- The recently discovered branches immediately below Y3120/YP196/S20602 are:
FGC12098 (FT76511), and it has only few members so far – from Serbia, Bosnia & Herzegovina (FT256359), and Poland (*). (https://www.yfull.com/tree/I-Y3120/ )
FT80992 which contains only two samples so far, one from Germany and one from Hungary.
- The subclade Y4460 has many representatives in northern Europe, and very few in the Balkans. Some of the Y4460 people in Ukraine, Belarus, Russia… are positive for the initial branches of this subclade, and all Y4460 people in Bulgaria, Montenegro, and Greece(?) belong to a couple of lineages formed 2100 years ago. (The surnames of Y4460 men from western Balkans, who are akin to Bulgarians, can be seen at https://bosnjackidnk.com/baza-bez-markera/ )
The diversity of Y4460 in Hungary and Romania is rather conspicuous, and when everything is considered (geographical position of the countries, historical context, the level of presence of this haplogroup in the Balkan countries), it is safe to say that western Dacia was the probable place from which Y4460 spread towards the north, west, and, to a much lesser extent, south.
However, what is even more conspicuous is the following: the younger branches (formed less than 2000 years ago), which represent the majority in eastern and western Slavic countries, have not been found in the Balkans! This could mean that:
In either case, this is the crucial piece of information: there was no subsequent migration of I-Y4460 people (in the 6th, 7th, or later centuries) to the Balkans which could have brought the younger branches.
- The oldest lineages of Y18331 are found in Greece, Albania, and Macedonia, while others are scattered mainly across the northern and eastern Europe. (https://www.yfull.com/tree/I-Y18331/)It is obvious where this Y3120 branch originated.
- The subclade S17250 was, according to the available data ( YFULL: id:YF15878BGR, id:YF14628BIH, id:YF07821BGR, id:YF06137 HUN) , formed either in the eastern Balkans or somewhere in the Romania-Serbia-Hungary border triangle, but something indeed extraordinary happened 2100-1800 years ago. As it is supposed, this is when the sub-branches PH908, Y4882, and Y5596 appeared. And, for now, it appears that PH908 developed in the western Balkan, and Y4882, Y5596 somewhere over the Danube (from Ukraine to Poland).
The following facts indicate that that Y4882 and Y5596 originated in the north: all lineages are there; in the south-eastern Europe Y4882 is represented with only one A1328 branch, and the percentage varies from 0 to 1.5% (of all haplogroups), while Y5596 is practically inexistent. The ancestor(s) of these people could have come to the Balkans with Avars, Slavs..., but also (and more likely) individually, and more recently – because of their small number.
Historically, the appearance of Y4882 and Y5596 can be connected with the Roman expeditions before and at the beginning of the Common Era – some S17250 men from Thrace or Dacia were surely deployed in Germania, but it could also be a result of an independent movement from Pannonia.
It is quite the opposite with PH908 – most basal lineages are in the Balkans (https://www. yfull.com/tree/I-PH908/ ); the diversity is remarkable; and it represents the vast majority of I2a1a2b population in Croatia, Bosnia, Serbia, and Montenegro (~2.500.000 men); This is the only Y3120 (S17250) subclade which should be called “Dinaric”.
There are two historical realities which support the Balkan origin hypothesis of PH908.
- All the data from YFull and various national DNA projects show that Z17855 subclade was undoubtedly formed in the eastern Balkans (https://www.yfull.com/tree/I-Z17855/ ) and most of its representatives still live in the same region. It seems that its “mild” expansion (together with the further expansion of I-Y4460, E-V13 and R1b lineages) towards the north started in the 8th century when "the Vlachs crossed the Danube and attacked the residing Slavs". With the arrival of Hungarians these people spread over a wider area. Some Z17855 lineages are confirmed in western Balkans too – for example, the members of the Vlach tribe called Mirilovići from Herzegovina.
 In order to realise the irrelevance of “number”, and limited relevance of “variety/diversity” arguments in this discussion, one should take a look at the following actuality: The population of Ireland is about 6.3 million, but it is estimated that at least 50 million people around the world have Irish forebears. Who came from where?
 Ćirković Sima – Herceg Stefan Vukčić-Kosača i njegovo doba, Beograd 1964.; Mužić Ivan – Vlasi u starijoj hrvatskoj istoriografiji, 28-30 (Split, 2010.); Željko Musović, Genetika, istorija i bajke, Internet Archive 2020.
 Neparáczki, E., Maróti, Z., Kalmár, T. et al. Y-chromosome haplogroups from Hun, Avar and conquering Hungarian period nomadic people of the Carpathian Basin. Sci Rep 9, 16569 (2019). https://doi.org/10.1038/s41598-019-53105-5;
*** This study is rather important because it undoubtedly shows that R1a men and I2a1 men (most probably Y4460 or Z17855) who lived in Panonia (modern Hungary) in the 9-10th century did not belong to the same ethnic group. Namely, apart from different autosomal and Mt-DNA results, it was discovered that 75%, or 3 out of 4 R1a (Z280-CTS1211) men were lactose tolerant, while 83%, or 5 out of 6 I2a (xS17250) men were not.
- Povijest minulih ljeta ili Nestorov ljetopis, 7, 16; preveo N. Kosović; BG 2003.
There has been no archeogenetic evidence yet that I2a1a2b haplogroup was present in the south-eastern Europe 1500-2500 years ago. (The oldest analyzed sample was from the 9th century (Serbia). And, there has been no archeogenetic evidence that it was present in any of the east or west Slavic countries (or anywhere else) at that time either.
But, the facts stated above indicate that a small number of I2a-Y3120 men could have lived in lower Danube region (Hungary, Serbia, Romania...) about 2100-2300 years ago. One theory proposes that those people came there from the area in which carriers of primary I2a-L621 lineages live today (Germany, Baden-Württemberg) under the influence of Celts (a tribal confederation called Volcae) who invaded Greece in 279 BCE.
As it happened, one or several of those (Celticized) Y3120 men had (at least) six sons who became the common ancestors of all present-day Y4460, S17250, Z18755, Y18331, FT80992, and FGC12098 people in the world. In the centuries that followed some of their descendants went to the north-west and some to the south-west. And, that is how modern “Carpathian” and “Dinaric” I2a1a2b branches came into existence.
Now, if you take a look at these maps:
you will easily see the correspondence between the territory with the highest I-Y3120 haplogroup frequency in Romania, and the territory of the Wallachian principality from the 14th century. The common denominator is obvious, isn’t it?
When this discovery is supplemented with the already presented information about numerous members of former medieval Vlach tribes and communities from Montenegro and Herzegovina who also predominantly belong to I-3120 subclades, the connection becomes undeniable – the expansion of I2a1-Y3120 haplogroup was correlated to the migrations of Vlachs.
And that is not all. This argument/connection does not apply just to the western Balkan. Remember the “Carpathian” I-Y3120 branch(es)? It is an acknowledged historical fact that Vlachs routinely migrated up along the Carpathians between the 13th and 18th centuries. Some of them settled in Moravia, some in Slovakia, and some in Beskid Mountains. Hence, today we have Laccy and Wolosi in southern Poland, Moravian Wallachia in the Czech Republic, and people named Blahnik, Blahovec who inherit I-PH908 haplogroup (Blah = Vlah)… Needless to say, those are the places where the frequency of I2a1a2b is the highest in these countries.
As for Ukraine, which is sometimes (without any corroboration) suggested as the “cradle” of I-PH908, the genetic connection of the I2a1 men from the Carpathian Mountains in Ukraine and the I2a1 Romanians and Moldavians was well documented in the study Populations of Transcarpathia and Bukovina on the genetic landscape of surrounding regions.*
And finally, last but not least, it should be pointed out that the word/name Vlach/Wallach (and other variants such as Vlah, Valach, Voloh, Blach, Oláh, Vlas, Ilac, Lah…) is etymologically derived from Wolkā-/Volcae/ Οὐόλκαι – the ethnonym of already mentioned Celtic tribe. Germans adopted the word in the forms Walhaz, walhs… (stranger). Via Latin, the ethnonym took on the meaning “foreigner”, “Roman” or “Romance-speaker”, and Greeks loaned it from Slavs (Vlah → Βλάχοι).
The rest is history… and genetics.
 Edvard Ehler, Daniel Vaněk, Vlastimil Stenzl, and Václav Vančata. Y-chromosomal diversity of the Valachs from the Czech Republic: model for isolated population in Central Europe. Croat Med J. 2011 Jun; 52(3): 358–367. doi: 10.3325/cmj.2011.52.358
 Utevska, Olga & Chukhraeva, M. & Agdzhoyan, Anastasiya & Atramentova, Lubov & Balanovska, E. & Balanovsky, Oleg. (2015). Популяции Закарпатья и Буковины на генетическом фоне окружающих территорий. Вісник Дніпропетровського університету. Біологія, медицина. 6. 133. 10.15421/021524.
*Two years later, the same Olga Utevska, a geneticist from Ukraine, wrote her dissertation paper in which she arbitrarily stated that the greatest diversity of I2a1a2b DYS448 = 19 (!!) haplotypes was in Ukraine and Belarus. She also implied that the carriers of I2a1a2b I-PH908 haplogroup came to the Balkans with the Slavs in the V-VI (?!) century CE from the area which is a part of today’s Ukraine. However, a simple comparative review of the presence/distribution of I-S17250-PH908 DYS448=19 SNP-s or subclades (formed 1700-1800 ybp) in the Balkan and Ukraine respectively clearly shows the magnitude of her error: https://www. yfull.com/tree/I-PH908/
 Tanner, Arno (2004). The Forgotten Minorities of Eastern Europe: The History and Today of Selected Ethnic Groups in Five Countries. East-West Books. pp. 203–. ISBN 978-952-91-6808-8.
Juhani Nuorluoto; Martti Leiwo; Jussi Halla-aho (2001). Papers in Slavic, Baltic, and Balkan studies. Dept. of Slavonic and Baltic Languages and Literatures, University of Helsinki. ISBN 978-952-10-0246-5.