The name “Era of Good Feelings” is often given to the time that began with the first election of James Monroe in 1816 and ended with the creation of the Whig Party. The term is also very often used to refer only to Monroe’s two terms in office.
There are two main reasons why this time got the name that it did. First, this was a time in which there was only one political party. The War of 1812 had killed the Federalist Party. This party had come to be centered in New England and New England generally did not like the war with England. There had even been the Hartford Convention in which secession from the US was discussed. When the US essentially won the war, the Federalists looked unpatriotic and lost their support. They soon folded as a party. With no interparty conflict, the era came to be called the Era of Good Feelings.
The other reason has to do with the win in the War of 1812. This win led to a new wave of nationalism. Americans came to have more price than ever before in their country. They had been able to win a war. They had a vast western territory to explore and exploit. Their economy was starting to get much stronger. All of these factors made Americans feel better about themselves and their country.