When people do this they put their heads so close together that they practically breathe each other's air. what is one word to describe that?

Well I doubt this is right, but based on the vocabulary packet this question came from I would say that the word is conspire.

Explanation:

because of all the immigration, america became one big melting pot. the diversity of cultures from all over the world made america somewhat divided as well. people that immigrated stayed with their kind, and their traditions, while native born americans stayed with their kind and their traditions. normally, people born in american scorned the immigrants as well. the new religions also divided america. in summary, it took away from the american culture and identified america as the "melting pot."

the answer is the last one