Here's the period of time we've discussed on Crash Course and this is how long we've had the technological capability to exterminate ourselves. So that's worrisome. Immediately after World War II, the Soviets created a sphere of influence in Eastern Europe, dominating the countries where the Red Army had pushed back the Nazis. Which is why Winston Churchill famously said in 1946 that an iron curtain had descended across Europe. While the dates of the Cold War are usually given between 1945 and 1990, a number of historians will tell you that it actually started during World War II. Japan's distrust of the US and Britain kept growing as they refused to invade Europe and open up a second front against the Nazis. And some even say that the decision to drop the first atomic bombs on Japan was motivated in part by a desire to intimidate the Soviets.