The US didn't get involved earlier because the people didn't want to fight. They were a 'Sleeping Giant'. Say thank you to the Japanese for waking up the US with the attack on Pearl Harbor [no offence to Japanese people].
The u.s. DID get involved.
1917
yes they were
No
yes
World War 2
There were 116,000 US casualties. 4,744,000 were involved.
The Neutrality Act
The US contributed some 16 million personnel to the Second World War. I'd say that would indicate they did get involved.
The United States became involved in the World War II about March 1941.
They didnt want to start a war
the US by FAR.