Which term is used for the moment when the groups that make up political parties are rearranged?

Realignment is when the groups that make up political parties are rearranged. In the US, when the balance of power between a country's political parties changes, they resort to party realignment. The groups of people who vote for them change drastically. This occurs when political parties either die out or are created. Realignments can be the outcome of major historical happenings. Likewise, they can also be the result of demographic changes.