The treaty of Versailles was an unfair one. The "war guilt" clause forced Germany and her allies to take all the blame for the world war. Moreover, Germany lost it's land, overseas colonies, population, and coal and iron industry. Germany was also made to pay reparations and limit their armed forces.
The treaty of Versailles was an invitation to deadlier wars in the future. In fact, it can be concluded that the treaty was a controversy in itself. Because Germany was subjected to ill treatment and was made to pay reparations beyond the country's capacity post war, it became the mojor cause for the WW II.
I don’t know if this is right but as someone who is native I’m going to guess during conversion of religion. Again I don’t know if that’s the main one they want but it was a contributing factor. :)
