Why did Great Brittian need Americas help in fighting off the germans?

Great Brittian begged for Americas help in fighting the germans and America didn't help at first but then finally went in. It seems that even Churchill himself tried to get the americans to help and said, "The Americans can be counted on for doing the right thing....after they've exhausted all the other possiblities." But what had happened to the Brittish army at this time that they needed America's help so badly? Had they cut funding to their defense in recent years previous to the event?