The League of Nations was an organization of countries that promised to work together to ensure another World War would not occur.
Germany was not allowed to join until 1926, and surprisingly, the U.S. refused to join. The U.S.' Senate refused to pass a vote to join the League of Nations because they believed that the treaty was too vague in its ability to enforce any of the rules that it made up, and they were concerned it would cause another war.
Germany was affected in many ways from the Treaty of Versailles and the League of Nations. Many Germans felt humiliated by having to admit sole responsibility for WWI and pay reparations. They opposed the restrictions and held protests.
The treaty cause great economic stress to Germany's economy and thrust them into a depression. Other countries continued to blame Germany and they became more isolated from them.
Although the Treaty of Versailles brought temporary peace, many believed that it caused Germany's turn towards Nazism and the rise of Adolf Hitler. Germans were angry, frustrated, and resentful of their global and economic situation. It created a platform where Hitler could promise the rise of Germany once again, and the German people wanted a return to their previous global and economic status before the first world war.