The successes of unions like the AFL had done some to ease American fear of the possibilities of revolt and revolution. However, the idea of radicalism, or extreme views on change caused by possible violence, were not over. In fact, in many ways they were just beginning to show themselves to the nation. Many radicals held strong beliefs that the problems in America were much deeper than conflict between workers and bosses. Instead, they began to question the very idea of capitalism.

Industry had grown up in an era of Jefferson’s “lassiez-faire capitalism”, in which the government stayed out of the way of businesses and small businesses and companies used the market to guide the economy. However, after the Civil War, companies began to grow and combine, and soon there were corporations and company owners who were controlling things. This was an abuse of capitalism sometimes known as “crony capitalism” or “corporate capitalism”. This, however, was not just an American condition. It was seen in Europe as well, including in the British Empire and the German states of Central Europe.

In reaction, some philosophers began to question the system completely and propose new ideas that were radically different. In Germany, two thinkers and activists named Karl Marx and Fredrich Engels proposed the idea of socialism. In the theory, the results of industry were poverty and oppression. Marx and Engels believed that the workers should say what happens, and that the people should collectively, or all together, own the means of production, which would lead to equal shares in the income made from farming and industry. Business owners, both small and large, would be allowed to own industry. The idea also evolved into communism, especially with the belief that government would need act to make the changes.

The ideas of Marx and Engels appeal to some American radicals. Many asked why so many working Americans should have so little while a few owners grew incredibly wealthy. No wealth could exist without the sweat and blood of its workforce. They suggested that the government should own all industries and divide the profits among those who created the products. While the current management class would stand to lose, many more people would gain. These radicals grew in number as industries spread. But their enemies were legion.

Eugene V. Debs, who had been very involved in the Pullman Strike, is considered the “Father of American Socialism”. Born to French immigrants, he worked his way through the railroad industry, and founded the American Railway Union in 1892. After his arrest and failure in the strike, he began to change his views. Debs was not originally a socialist, but his experience with the Pullman Strike and his subsequent six-month jail term led him to believe that action was necessary. Debs chose to stick to politics. In 1900, he ran for President as a socialist and gained almost 87,000 votes.

The next year, leading sympathizers joined with him to form the Socialist Party. At its height, the party had over 100,000 active members. Debs ran for president four more times. In the election of 1912, he received almost a million votes. After being arrested for anti-war activities during World War I, he ran for president from his jail cell and polled almost a million votes again. Debs died in 1926 having never won an election, but over 1,000 Socialist Party members were elected to state and city governments.

Even more radical than the Socialists were the members of the Industrial Workers of the World. The IWW, or “Wobblies”, believed that compromise with owners was not an option. Founded in 1905 and led by William Haywood, the union encouraged their members to fight for justice directly against their employers. Although small, they led hundreds of strikes across America, calling for the overthrow of the capitalist system. The IWW won few battles, but their efforts sent a strong message across America that workers were being mistreated.

When the United States entered World War I, the "Wobblies" launched an active anti-war movement. Many were arrested or beaten. Membership declined after the war, but for two decades the IWW was the center of radical American activism.