Although the Populist Party attracted a fair degree of support for its policies, it was never able to appeal to a broad swathe of American voters. As a result, the party was never able to establish itself as a truly national force in American politics able to compete with the Democrats and the Republicans.

The 1894 mid-term elections were very disappointing for the populists. This led some of their number, who would eventually be known by the name of “fusionists,” to argue for a formal merger with the Democratic Party, which had suffered a calamitous defeat in the 1894 mid-terms.

However, not all populists were supportive of the merger proposals. The radical wing of the movement wanted the party to remain independent. Only that way, they believed, would they be able to offer the American people a genuine alternative to the established parties. Such radicals clearly understood that a merger with the Democrats would involve a watering-down of their plans for root and branch economic reform and public ownership of railroads.

In the event, the radicals prevailed, generating a huge split in the populist movement that, along with other factors such as an improving economy, sounded the death knell for the Populist Party.

The Populist Party (or people's party) was popular because it supported farmers in the South and West who were suffering from declining prices, high interest rates, economic depressions, droughts, and an unpredictable market.  The populist party gained national attention when they supported Democratic nominee William Jennings Bryan as their presidential candidate.  

One of the reasons this led to a decline in the populist party is because nominating Bryan alienated the African-American populists.  The African-Americans argued that the democratic party failed to support them in the South.  The white populists ignored their appeal and supported Bryan.  When Bryan lost to Republican William McKinley in the election, the populist movement took a major hit.  

Additionally, right about this time, gold and been discovered out west, which renewed the economy and helped many farmers in this region, who had previously relied on the populist party to fight for their prosperity.  Now that the economy was picking up, the populist party wasn't needed anymore.  

Ultimately, the populist party merged in with the Progressive Party, which had a much larger audience (all working class as opposed to just farmers in the South and West) and was more successful in achieving goals for its supporters.

The populist movement ended for two main reasons.  First, it was unable to get enough people to support it.  It was never really able to expand its base past the farm communities of the South and West.  It was never able to make inroads among the workers and among the middle class.  Second, the populist movement was absorbed into the Progressive movement.  The Progressives were able to take populist ideas and integrate them into a bigger movement.  The Progressives had a much bigger agenda and were able to appeal to workers and to the middle class.  Therefore, they were better than the populists at achieving populist goals.  This helped them to be successful and made the populists irrelevant.