That period of time is called the "wrath" of God. The tribulations that Christians have gone through are not the result of God's "wrath". It's the "wrath" of God that Christians have been promised to never have to endure.
What a great point. Walvoord also points out another aspect of the Great Tribulation that seperates it from the tribulations we suffer now.
From the article:
The great tribulation is always presented in Scripture as a future time of trouble while the state of difficulty and persecution experienced by the early church was clearly contemporary.
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