It shows occurrences of the phrase "[any noun] crisis" (eg. housing crisis, migrant crisis) per million two-word phrases (known as 2-grams or bi-grams) published in English-language texts. The latest available data is from 2008. Crisis peaked in the mid-1970s, remained high throughout the 1980s, but has fallen swiftly and steadily over the past 20 years. On the other hand, it seems we don't need a crisis to declare a war (or vice versa). Our penchant for declaring war on stuff has never been stronger, with declarations of "war on [random noun]" since 2001 eclipsing war talk during both World Wars. They're represented by the first two peaks on the graph. (We'll get to that third one in a moment.)

Things get more intriguing when we break them down. Here are the top 10 nouns we declared war on over the past century. We really didn't like Germany (shown in orange) for a long time there – pretty much for the entire first half of the 20th century. Poverty (blue) was enemy number one during the hippy heyday of the 1960s – that's the third bump in that second chart – but by the 1990s, our guns were pointed at a new foe: drugs (yellow). The flat and falling lines of the 1980s and 1990s suggest that by the turn of the century, we were a society in search of a new adversary.

And find one we did. No enemy of the previous century comes close to our 21st century foes, terror and terrorism. Clamour about terror and terrorism was three times as loud in 2008 as mutterings about Germany at their peak in 1944. As for crises, the chart below suggests we began the 20th century looking boldly outwards but have since retreated inwards. Doom and gloom warnings about world crisis (shown in orange) dominated from the first World War through to the 1956 crisis in the Suez canal (pink). Missile crisis (yellow) topped the chart briefly in the late 1960s (think: Cold War and Cuban missile crisis), before it was dwarfed by the century's worst crisis: the energy crisis. (The term "oil crisis", shown in red, refers to the same series of shocks to the West, set into motion by the 1973 Arab oil embargo.)