A popular front is "any coalition of working-class and middle-class parties", including liberal and social democratic ones, "united for the defense of democratic forms" against "a presumed Fascist assault". More generally, it is "a coalition especially of leftist political parties against a common opponent".
The term was first used in the mid-1930s in Europe by communists concerned over the ascent of fascism in Italy and Germany, which they sought to combat by coalescing with non-communist political groupings they had previously attacked as enemies. Temporarily successful popular front governments were formed in France, Spain, and Chile in 1936.
Not all political organizations who use the term "popular front" are leftist or coalitions formed to defend democratic norms (for example Popular Front of India), and not all leftist or anti-fascist coalitions use the term "popular front" in their name.
Terminology and similar groups
When communist parties came to power after World War II in the People's Republic of China, and the countries of Central, and Eastern Europe, it was common to do so at the head of a "front" (such as the United Front and Chinese People's Political Consultative Conference in China, the National Front in Czechoslovakia, the Front of National Unity in Poland, the Democratic Bloc in East Germany, etc.) containing several ostensibly-noncommunist parties. While it was the communist party—not the fronts—that held power in these countries, the alleged coalitions gave the Party the ability to maintain that it did not have a monopoly on power in that country.
Another use of the word "front" in connection with communist activity was "Communist front". This phrase used "front" not in the sense of a political movement "linking divergent elements to achieve common objectives", but as a facade "used to mask" the identity/true character/activity of "the actual controlling agent", (examples being the World Federation of Democratic Youth, International Union of Students, World Federation of Trade Unions, Women's International Democratic Federation, and the World Peace Council). Communist front was a label frequently applied to political organizations opposed by anti-communists during the Cold War.
The strategy of creating or taking over organizations that would then claim to be expressions of popular will, and not manipulation by the Soviet Union or communist movement, was first suggested by Vladimir Lenin. These would not be political coalitions seeking power in opposition to fascist movements, but groups designed to spread the Marxist–Leninist message in places where the Communist party was either illegal or distrusted by many of the people the party wanted to reach. It was used from the 1920s through the 1950s, and accelerated during the popular front period of the 1930s. Eventually there were large numbers of front organizations.
Comintern policy: 1934–1939
The international communism, in the form of the Communist International (Comintern), the international communist organization created by the Russian Communist Party in the wake of the 1917 Bolshevik Revolution, went through a number of ideological strategies to advance proletarian revolution. Its 1922 congress called for a "United Front" (the "Second Period") after it became clear proletarian revolution would not sweep aside capitalism in the rest of the world, whereby the minority of workers who supported communist revolution would join forces against the bourgeoisie with workers outside the communist parties. This was followed by the "Third Period" starting in mid-1928, which posited that capitalism was collapsing and militant policies should by rigidly maintained, As the Nazi Party came to power in 1933 in Germany, and annihilated one of the more successful communist movements in that country, it became clear fascism was both on the rise and saw Communism as an enemy to be destroyed, and that opposition to fascism was disorganized and divided. A new, less extreme policy was called for whereby Communists would form political coalitions with non-Communist socialists and even democratic non-socialists – "liberals, moderates, and even conservatives" – in "popular fronts" against fascism.