1> All time greatest achievement Technology
2> 20th Century's greatest achievement Films, music, dancing
3> So far the greatest achievement of 21st Century War on terrorism
4> All time worst achievement Terrorism
5> 20th Century's worst achievementnothing
6> So far the worst achievement of 21st Century Obama, because everyone follows him blindly without realizing that number 1, his skin color doesn't matter (TheOtherLeadingBrand), number 2, he's Muslim and hates America, number 3, he'll run this country into the ground.