Ashkenazi Jews
Although strictly speaking, “Ashkenazim” refers to Jews of Germany, however the term has come to refer more broadly to Jews from Central and Eastern Europe. Jews first reached the interior of Europe by following trade routes along waterways during the eighth and ninth centuries. Historical evidence indicates that Jewish communities began to spread into Europe during classical antiquity and migrated north during the first millennium CE, arriving in the Rhineland by the 12th century. Local European women could have begun to join the Jewish population around 2,000 years ago or earlier, Richards and colleagues suggest, and the Ashkenazis may have continued to recruit additional women as they headed north.

 Many Ashkenazi Jews moved to the Polish Commonwealth (today’s Poland, Lithuania, Latvia, Ukraine and Belarus), where their skills and education were welcomed. The small preexistent Polish Jewish community’s customs were displaced by the Ashkenazic prayer order, customs, and the Yiddish language.
The influx of German migration to North America in the 19th and early 20th centuries accounts for the Ashkenazi predominance in tradition and liturgy. The modernization The  culture of Poland, Russia, and Lithuania produced a constant stream of new Talmudic scholarship. In 18th-century Germany, the Hashkala movement advocated for modernization, introducing the modern denominations and institutions of secular Jewish culture. This movement is the root of the denominations in North America.
Ashkenazim are the most populous ethnic group in North America. The modern religious denominations developed in Ashkenazic countries, and therefore most North American synagogues use the Ashkenazic liturgy. 
Perhaps Ashkenazi customs are most exemplified by Matzos Ball Soup and Gefilte Fish. For more information about Ashkenazi cuisine visit My Jewish Learning Center
Some maerial excerpted from The Scientist Magazine and My Jewish Learning Center