Party realignment in the United States

A party realignment in the United States is when the country transitions from being mostly run by one political party to mostly run by another political party. During party realignments, some groups of people who used to vote for one party vote for the other one. Sometimes, political parties end and new ones begin. Party realignments can happen because of important events in history or because of changes in the kinds of people in the country. 
1820s.
In the early 1800s, America had the "First Party System" with the Federalist Party and Democratic-Republican Party. When James Monroe was elected President of the United States, the Federalists died out. There was an "Era of Good Feelings" of one-party rule by the Democratic-Republicans. In the United States presidential election, 1824, four different men ran for President, all as Democratic-Republicans. John Quincy Adams was elected. 
After the election, Andrew Jackson formed a new party called the Democrats. Jackson's party was strongest in the South and West, and in some cities (at this time, only a few Americans lived in cities). Soon after Jackson's election, another party formed around supporters of Adams and Henry Clay. It was first called the National Republican Party, and later the Whig Party. The Whigs were strong in the North, and among the middle class and businessmen. The system of Democrats and Whigs is called the "Second Party System."
1850s-60s.
After the Kansas-Nebraska Act, the "Second Party System" ended: 
1930s.
America went from being mostly Republican in the 1920s to mostly Democratic in the 1930s. This was due to America becoming much more urban, and the Great Depression. Franklin D. Roosevelt formed a coalition that would mostly last until 1964 called the "." 
1960s-80s.
In the 1960s and 70s, the New Deal coalition fell apart. This was due to the Civil Rights Movement, Roe v. Wade, Vietnam War and the suburbanization of America. What changed: