European languages
The most important cause of European genetic variation corresponds to the migration of Neolithic farmers from the area of origin of agriculture in the Middle East.
The next most important component of genetic variation is apparently associated with a north-south gradient possibly due to adaptation to cold climates but also to the differentiation of the Uralic and the Indo-European language-speaking people.
The third component is highly correlated with the infiltration of the Yamna ("Kurgan") people, nomadic pastoralists who domesticated the horse and who have been claimed to have spread Indo-European languages to Europe.
References
Piazza A, Rendine S, Minch E, Menozzi P, Mountain J, Cavalli-Sforza LL. Genetics and the origin of European languages. Proc Natl Acad Sci U S A. 1995 Jun 20;92(13):5836-40. PMID: 7597038