The war guilt clause required Germany to accept blame for the war, pay reparations to the countries it fought against, and severely reduce its military.
The Treaty of Versailles, which came out of the Paris Peace Conference, was very punitive towards Germany. Germany was forced to admit responsibility for causing the Great War (World War I) -- what we now call "the war guilt" clause of the treaty. Germany also was forced to pay large reparation payments to the Allies (who opposed Germany in the war). In addition, the German military had major restrictions imposed on it -- it had to be a volunteer military only, of no more than 100,000 men, and they could not have an air force.
The German economy and national pride were deeply wounded. The Great Depression devastated Germany -- even worse economic conditions than in America at that time. The bad situation in Germany made it possible for a radical leader like Hitler, making all sorts of bold promises, to win over enough people to rise to power.
