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So, the time of trouble (i.e., Jacob's Trouble (Jer 30v7)/The Great Tribualation) such has never been since there was a nation is still future for Dan 12v9 tells us it occurs at 'the time of the end' and such a time has NOT occured as yet; Dan 12v7 tells us that this period of time also know as the Great Tribulation is 'a time, two times and half a time' three and a half years, so you quite wrong to say that the time period that the Great Tribulation lasts is not given in Scripture, for as I have shown it is, it last three and a half years!
The above scriptures indicate a time coming on America and Great Britain. Since they are the direct descendants of Jacob ( Israel) this will be a time like no other for them. We are entering that time frame now.