The Achilles heel of Reformed theology is eschatology. John Calvin failed to include a commentary on the Revelation in his other commentaries, leaving the door wide open to later Reformed theologians in the area of eschatology. The high point of American Reformed influence came in the mid-nineteenth century when Post Millennialism was wildly popular and was proclaimed from the Reformed pulpits and sung lustily in hymns such as "Mine Eyes Have Seen the Glory of the Coming of the Lord." The concept was quite easy - eliminate the evil of slavery from America and the Millennium would commence.
Unfortunately, despite the gruesome Civil War the Millennium failed to develop. Instead there were major financial panics in 1873 and 1893 with subsequent economic depressions.
Not to be dissuaded, Reformed theologians regrouped and determined that the issue preventing the Millennium was the production and consumption of alcohol. When America achieved righteousness in eliminating alcohol, then the Millennium was bound to begin. In fact, one of the leading Reformed publications at the beginning of the twentieth century was called "The Christian Century" for that reason. So what happened? The Prohibition of alcohol was enshrined in the American constitution. Then came World War I with its disastrous consequences. Then came the Roaring Twenties with loosening morality. Then came the Great Depression and the repeal of Prohibition. Then came World War II. By then Reformed eschatology (specifically Post-Millennialism) was in complete tatters and most Reformed denominations had completely abandoned eschatology entirely, limiting themselves to rants against Dispensationalism.
Today, a few Reformed folks are attempting to develop some form of alternate eschatology to Dispensationalism. Preterism, in various forms, has been attempted and has generally been rejected. That pretty much leaves amillennialism in a very generic form, which isn't much to hang your hat on.
