Irrigation of the crops led to salinization of the soil, Sumer was located on a flat plain that provided no natural barriers to invasion, and the land became to swampy to grow adequate crops.
Germany believed it could win the war before the United States could fully mobilize its military and they no longer had to battle on the Eastern front after Russia withdrew.
HOPE IT HELP ;)
Goes through the House of Representatives and the Senate
I was built by the assembly line method of production. Hope this helps.:]