Because after WW2 communism in the Soviet Union started to grow, so a lot of the western European countries (Italy, France, Great Britain, etc) joined together along with the US to face communism.
To protect the sovereignty of the European nations, that had not already been declared as conquered territories, by the Soviet Union.
cause they needed more help in polacy
So that during wars they could go fight for and protect Eastern Europe.
One reason is that people at the time were deeply religious, and were told that if they went on these "holy" missions to retake Jerusalem they would receive penance, forgiveness of their sins.
In World War 1, The United States did not get involved at first because none of the issues concerned the United States. Besides, The United States had a long history of not getting involved in wars that did not specifically involve the United States. European nations had been fighting for centuries. Let them continue to fight. Also, each European Nation had a specific reason for fighting. The United States had no reason to get involved.
because the confederate states were actually another nation since they had a constitution and all that. therefore the southerners were angry when they joined the united states again and the northerners couldn't believe the nation had been divided and they didn't trust the southerners.
socialism
Western European nations encouraged Immigration to make up for their declining populations
Western European nations encouraged Immigration to make up for their declining populations
Western European nations encouraged immigration to make up for their declining populations
Romania and Bulgaria are members of the European Union from 1 January 2007.
They feared it could lead to future U.S. involvement in European Wars .
to bring europe back together again
Africa had a wealth of Natural Resources
So that during wars they could go fight for and protect Eastern Europe.
Independence turned violent where european colonists settled.
The US didn't want to get caught up in European affairs that had nothing to do with them again.
One reason is that people at the time were deeply religious, and were told that if they went on these "holy" missions to retake Jerusalem they would receive penance, forgiveness of their sins.
Virtually all of the countries of the world. I think a notable exception is Switzerland. For some reason the flag of Macedonia is not flown at the UN..... Switzerland joined September in 10th 2002. The full list of Member States of the United Nations with the date on which they joined the Organization can be found at http://www.un.org/members/list.shtml. At the time of writing this answer there were 192 members.