| This concept has been used by the military for decades primarily in wargaming. |
| The biggest difference is that over the past two decades the United States has absorbed roughly 20 million immigrants. |
| For decades the prevailing theories tell us that the roots of violence lie in deprived environments and abusive parents. |
| Several decades of time have passed by as quickly as the clouds have been blown away. |
| Romney's father, who was a Republican, too, but governor of Michigan, ran, if disastrously and abortively, for president almost four decades ago. |
| Since in vitro fertilization started, two decades ago, there has been an explosion of twins, triplets, quadruplets, even quintuplets. |
