Why was the US hesitant to enter World War 1?

The US had no reason to enter the war prior to 1917. No American interests were at stake, and the country was doing very well from trade with the Allies, leading to great prosperity. There was some distress at American passengers on allied ships (eg the Lusitania) being killed when these ships were torpedoed, but most Americans did not regard this as a justification for war, since nobody had compelled the Americans to take the risk of using belligerant ships. The position changed after January 1917, when Germany declared unrestricted U-boat warfare, and began sinking all ships in allied waters, including American ones. After three American ships had been torpedoed, and it was revealed that Germany had sought alliance with Mexico against the US, opinion moved rapidly in favour of war.