How did confederation in Canada happen?

Confederation happened because political deadlock from Canada East and Canada West lead to political deadlock, leading to the Great Coalition, which was in favour of Federal Union. A railway was needed to connect the colonies, trade, and send troops faster. Threats of Americans invading British North America caused the colonies to want to unite and become stronger. People wanted to settle Rupert's land and the Northwest Territories. America cut off the Reciprocity Treaty, therefore making it expensive to trade with them and so Canada began to trade among themselves without paying taxes. Great Britain wanted her colonies to be more self-sufficient and have them do things by themselves.