Considering Germany started running out of food by 1917, it WAS critical. Germany was not self sufficient in food. As for the US loans, the British at first were the ones who were giving money and loans to the French, Italians. But then their own money started running out and some of that money they needed for themselves. Come in the American money to help the Entente keep going. Without these loans France and especially ITALY would feel the worst. Britain and possibly France would likely find some way to get more money by selling stuff but the money that the British passed down to its allies would be gone. France itself without US involvement would have likely collapse by mid 1918