29. A Giant Customs Barrier
Northern India has relatively few sources of salt, and throughout most of history, the region had to import it from elsewhere in the subcontinent. When the British conquered India, they hit upon the idea of cashing in on that by monopolizing salt production, then gouging the natives for all they could get out of them via stringent salt taxes.
The salt tax proved hugely unpopular with the Indian public. Protests over its collection helped fuel the rise of Indian nationalism and sowed the seeds of India’s independence movement. More immediately, however, the British had to contend with rampant salt smuggling from southern India, where salt was abundant and salt taxes were low, to northern India, where the opposite was true. So came up with the idea of growing a giant hedge of thorn bushes, stretching across India for thousands of miles.