Why did immigrants usually band together in groups of their own ethnicity?

Language can be the most common factor.

Explanation:

The migrant route implies many difficulties when people go to the desired destination. Europe currently has a big problem with the migrant crisis, considering that due to wars and economic factors, many people from the countries of the Middle East want to reach Western Europe. Migrants most often move in groups, and these groups mostly consist of migrants from the same country. This phenomenon is most often language since migrants thus communicate with each other more easily. The reasons are also cultural, given that migrants in the same groups share common cultural values from their home country.

the first question's answer is a.