According to Strong's Concordance, tribulation means: 1. a pressing, pressing together, pressure 2. metaph, oppression, affliction, distress, straits. I don't hesitate to say we are already in tribulation according to this definition. There is more scriptures that talk about the tribulation of the saints than there is about any "world" tribulation. How does a saint overcome, except by enduring pressure. Pressure makes weight lifters strong. Without it they could never build muscles and strength. The same applies to the saints. Without affliction, pressure, etc. they would never have the strength to overcome.