Due to globalization your question should be, "When will we enter the next dark-age?" because our nation has been through much worse then we face today and has survived. If nothing is done to prepare for it, the next dark-age will begin at the end of this current carbon-age. Our civilization runs on fossil fuels, oil, natural gas, coal, etc., current estimates put our supply at between 75 to 150 years.
look at Rome once the corruption took hold like it has in the US it wasn't to long within 200 years there wasn't much left to Rome and with the people becoming weary already it's just a mater of time and that will create world wide changes good or bad don't think it's unavoidable