Party Realignment: Why Do Political Parties Change Or Party Realignment?

Party Realignment is when the balance of power between a country’s political parties changes greatly or when the voters change dramatically as well. This can happen when political parties die out or when new ones are created. This happens often every time election season comes depending on the party and what they are standing for. Voters tend to change sides based on what the party is standing for every election season. The Democratic and Republican parties have been easy to maintain
Throughout the years including the civil war years for many reasons. Out "first past the post" electoral system tends to lead to long-lived parties. Britain's Conservative Party dates to 1830, Canada's Liberal Party to 1867 which was when the country was formed. Australia's Labor Party since 1891, and Britain's Labour Party since 1900. So perhaps the real question is why the Federalists and Whigs were so short-lived compared to the Democrats and Republicans.
In any case, the long-term success of these two parties is based largely on two reasons: One being coalition and the other being adaptability.
By "coalition" I mean
The Republican Party, which was once a radical progressive party, is now today the conservative party. The Democrats, haven to white supremacists in the late 19th and early 20th centuries, is today the party most blacks identify with. Some of these changes are gradual, while others tend to move fairly quickly for example, Reagan's rise within the Republican party essentially chased all the "Rockefeller Republicans" out of the party in roughly a decade . This allows each party to stay current; without it, the Democrats would almost eventually have disappeared at some point during the 20th century as racism became less and less popular, and the Republicans might very well have dissapeared soon after the Civil War, since their original reason for being (the abolition of slavery) was by then accomplished