the US didnt really do much in WW1, they basically worked out a peace treaty, that in turn lead to the rize of to socialist party in germany, which borrowed largely from jewish banks and when thier economy started to decline sharply the nazi side of the socialist party came out and WW2 came about.
then the US really didnt do much in WW2 until the bombing of pearl harbour which was being used by allied forces as refueling and re-supplying base, after that america joined the war but mostly against the japs, in the process comiing some pretty nasty crimes against humanity nuked Nagasaki and then hiroshima to prove u could do it twice . it was actually the russians that ultimately took berlin, they also lost more soldies and civilians than everyone else combined. alot of which was due to their policies concerning the eastern blok . after taking berlin they gained alot of nazi nuclear research, and had already invested alot of money into thier armed forces which ultimately led to the cold war including korea and vietnam