When was the truman policy first used?
the greek civil war in 1947
the hungarian revolution of 1956
the vietnam war in 1964
the coup in iran in 1953

your answer is

to dominate europe

and i know for a fact it can't be the others

genetics is the study of how dna works, the methodologies defining the new recent technologies allow scientist to have a panoramic view of the entire dna landscape, especially how genomes interact with their environment, including off course, factors outside their organisms.

thus is very possible the existence of both scenarios, where populations of isolated individuals have different genetic traits, and share traits related to genetic mutation, due rats can easily travel overseas using human transport channels. so scientists could get a vast number of data, including human interaction, evolution of rodents, health development, spread of infections, development of new organisms, how genomes evolve in different environments and so on.

native american contribution: the patriots from britain learn how to hunt, fish, and introduce diversity within cultures.

african americans: indirectly introduced the idea of diversity to americans. africans coming to america because of slavery taught white americans that people come from different backgrounds and colors. it also built america's economic stability for a great period of time. 

women: make america what it is today. there are some societies that are in the world currently that do not give women the same right we give women here in the united states. because women have rights here in the united states, other countries' citizens strive to come to america, especially women, since they have equal rights in the united states. this is important because america is seen and desired by many in the world. 

children: children are our future. we learn from our elders and carry out things the same or differently learning from america's history. we continue tradition and change tradition if it is needed.