Why does gerrymandering occur?

It is mostly used to favor a political party in elections. In the US, it has been used during our entire history, from the Federalists and Anti-Federalists. Today, both Democrats and Republicans have used it. It has also been used to both increase the political power of minorities but also disenfranchise minorities. There have been several US Supreme Court cases dealing with gerrymandering and has resulted in several states adopting non-partisan redistricting committees.