1859 British minister John Nelson Darby begins preaching in America. He would create an ingenious theology known as premillennial dispensationalism, which remains the dominant eschatological system in Christianity today. "Dispensationalism" refers to Darby's belief that human history can be divided into a series of epochs, or dispensations, in which God has dealt with humanity in different ways. Darby teaches that biblical prophecy refers to the past and future periods, but is silent on the present "Church Age," which began with Christ's crucifixion. By asserting that God's prophetic clock had temporarily stopped ticking, this "Great Parenthesis" ingeniously preserves prophecy while avoiding the risks of date-setting.
One of the most enduring elements of Darby's system is the Rapture, in which true believers in Christ would travel instantly to heaven, where they would watch the terrible seven-year Tribulation unfold on earth, killing all but a righteous few. His emphasis on the Jews' return to Palestine and his strong reliance on scripture over church authority have also won favor with fundamentalists.
Rapture The belief that true believers in Christ will be taken bodily into heaven just prior to or during the Tribulation period, and thus be spared the horrible fate awaiting those left behind on earth. The rapture is an integral part of the premillennial dispensationalist systems which have dominated Christian prophecy belief in the second half of the 20th century, as it proposes faith in Christ as the only route to salvation.
Tribulation A period of upheaval, usually seven years in length, during which Satan will exert control over the earth through the antichrist. All but a small remnant of Christian faithful -- perhaps numbering 144,000 -- will die as a result of wars, plagues, and famine. The Tribulation will end with Christ's defeat of the antichrist at Armageddon, ushering God's millennial kingdom on earth.
http://www.pbs.org/wgbh/pages/frontline/shows/apocalypse/etc/cron2.html
http://www.pbs.org/wgbh/pages/frontline/shows/apocalypse/etc/glossary.html#Premillennialism