Ersatz means substitute, and English borrowed the word from German in the 1870s. In the First World War the blockade made the shortage of raw materials in Germany much worse. Yarn was spun from paper. Wooden soles replaced leather soles. By far the most important substitute was nitrogen, taken from the air by the Haber-Bosch process.
The habit is older. After the Seven Years’ War ended in 1763, Prussia planted large fields of chicory near Berlin, Breslau and Magdeburg. Coffee made from chicory could be grown at home instead of importing expensive coffee beans. Thirty years later there were 19 factories for Preußenkaffee, Prussian coffee.