Pentecostalism is a branch of Christianity, specifically of the Protestant evangelical variety.
Pentecostalism was established in the early 20th century in Los Angeles. In its early days it was actually a progressive denomination largely followed by poor people, who congregated in totally desegregated gatherings, railing against racism, nationalism and wage slavery. They did believe very strongly in an imminent apocalypse (see Christian eschatology). From the Jacobin article:
More than a century ago, Pastor Charles Parham, one of the founding fathers of Pentecostalism, even professed faith in the secular prophecies contained in the Communist Manifesto — up to a point.
“We are facing an international struggle wherein the governments, the rich, and the churches will be arrayed on one side,” he proclaimed in a sermon in 1911. “On the other side, will stand the masses of wage slaves who have been ground under the iron heel of oppression, whose lives have been exploited by industries and sweatshops until their whole being cries out for revenge.”
Parham predicted that an ultimate international class struggle was imminent, one in which the working classes of the world would “avenge themselves on their exploiters and the ungodly profiteers.” Where Parham strayed from Marx is that he predicted that a class war would lead not to the “dictatorship of the proletariat” but to Armageddon.
Unfortunately its progressive history has not lasted in the developed West (case in point: Scott Morrison). Pentecostals have generally become a much wealthier group than what they started as, with a concomitant change in their political values. In the 21st century USA, they have become a voting block for the Republicans, due to their conservatism on issues like abortion and gay rights. This is even though Pentecostals spent the 20th century abstaining from electoral politics, which they saw (at best) as a distraction from their holy mission.
Modern-day Pentecostals tend to ascribe to a doctrine known as the “prosperity gospel”, which holds that God rewards the faithful with riches and punishes sinners with poverty, so conveniently for right-wingers, you have no moral obligation to push policies that redistribute wealth more equitably, or even alleviate poverty and suffering, because they think people who are struggling deserve their lot.
In Latin America, though, Pentecostals have voted for left-wing candidates in numerous presidential elections (but not, seemingly, in Brazil). So outside the developed West, their progressive history is perhaps not so dead and buried.
Pentecostalism is now the denomination of a full quarter of the world’s Christians (so 500 million people), apparently. The denomination has made particular inroads in Africa and Latin America; for example, 30% of Brazilians now identify as Pentecostals. It’s not so popular in Australia, with only 1.1% of our population identifying as Pentecostal on the 2016 census.