The protest that sparked India’s collective revolt against British rule was Gandhi’s Salt March, in which he walked 240 miles to the ocean to pick up some salt. Britain’s rule in India was so heavy-handed that they literally made it illegal for Indians to pick up salt. British salt producers had lobbied the British government to shut down all Indian salt production, forcing Indians to buy expensive British salt.

The ability to preserve food gave fishers the ability to travel farther and farther. Previously, they were limited to the waters near markets. You only have so much time before a fresh catch begins to rot. Salt enabled them to travel deep out into the sea, where fish were more abundant.

As an ancient emperor, if you controlled the salt, you controlled the population. Since everyone needed it to survive, any fee on salt essentially became a head tax, which is a uniform tax imposed on everyone. Taxes like these were controversial, though, because the wealthiest citizens paid the same price as the poorest ones.

Aside from the fact that salt is an input for making gunpowder, it was also a strategic resource for war efforts. Without salt, you couldn’t preserve food for your soldiers. Any warring group without easy access to salt was at a major strategic disadvantage. This is exactly what happened to the South during the American Civil War. Early on in the war, Lincoln imposed a blockade on all Southern ports, which crippled their salt supply, because they imported most of their salt.