This rise in unemployment planted the seeds of the coming Great Depression. America also didn't gain very much from the war. The US didn't gain any land or materials unlike France and Britain. What they did gain was respect as a superpower and a military force.
If America had not entered the war against the central powers the war might not have gone in the allies favor. America claimed neutrality very early in the conflict in Europe, but they used the term neutral very loosely. America gave Britain much more support with supplies then Germany, if they stayed truly neutral and help both the central powers as much as the allied powers or didn't help either, the allied powers might have been in trouble. World war 1, like many other wars, lasted much longer and costed more than either side expected. This turned out badly for both sides as their supplies and available troops slowly got lower and lower. Germany did little to regulate the economy for a wartime footing, and