From Tom Reiss’s “Imagining the Worst: How a literary genre anticipated the modern world” (The New Yorker [28 November 2005]: 108):
… the first mini-boom in invasion fiction began in the seventeen-eighties, when the French developed the hot-air balloon. Soon, French poems and plays were depicting hot-air-propelled flying armies destined for England, and an American poem from 1784 warned, “At sea let the British their neighbors defy– / The French shall have frigates to traverse the sky. … If the English should venture to sea with their fleet, / A host of balloons in a trice they shall meet.” A German story published in 1810, and set in the twenty-first century, describes human populations living in deep underground shelters, with shops and churches, while balloon warfare between Europeans and invading Asian armies rages in the skies above.