What caused the American Civil War to break out? Was there one factor that caused more conflict leading to the American Civil War?

There were multiple factors that led to it.

The “stepping stones” that caused tensions to rise:
1: People in the North wanting to ban slavery.
2: People in the South wanting to keep slavery around.

The reasons that directly led to the war:
1: Abraham Lincoln being elected as the president of the US.
2: The South seceding from the North and making their own country.

In 911, a group of vikings lead by rollo besieged paris and chartres. after a victory near chartres on 26 august, charles decided to negotiate with rollo. the talks were led by hervé, the archbishop of reims. this resulted in the treaty of saint-clair-sur-epte, which granted rollo and his soldiers all the land between the river epte and the sea. it also granted him brittany, "for his livelihood". at the time, brittany was an independent land which france had not been able to conquer. in exchange, rollo promised the king his loyalty and military assistance when needed. also rollo also agreed to be baptised and to marry gisela, the king's daughter. the territory given rollo is about the same as upper normandy. this would grow to become normandy under rollo's descendants. - wikepedia