Had Germany had representation during the creation of the treaty they could have had better terms. They would speak about how they did not start the war.
With Germany present the German people would have less anger toward the other nations. Also this would have caused Hitler more trouble to rise to power if he was one of the few to really hate the Allies.
With Germany having to pay less war in war dept and having time to gather the money Germany's economy would be a lot better and they would not struggle. Hitler would not come to power as their would be less hate toward the European Countries and so the Nazi party would never be formed.