There were many factors that contributed to the defeat of the Central Powers during WWI.:
1- Failure of the Schlieffen Plan: this made Germans fight in two fronts.
2- Naval powers: the naval powers of the Allied were superior to those of the Central Powers.
3- Failure of the Submarine Campaign: that brought the USA into the war.
4- Political leaders: the political leaders of the Allied were much more competent than the leaders of the Central Powers.
5- German great losses.