Tariffs (and retaliatory tariffs) can be universally economically negative and still be rationally pursued by individual politicians.

For example: if Donald Trump tariffs the country you are in charge of, you are likely willing to pay the economic cost of a retaliatory tariff to seem like you are standing up to America to your constituents. The politician’s goal is to be re-elected.

The politician may aim to deter getting tariffed in the first place, and promising a retaliatory tariff if another country tariffs you first is also reasonable as a deterrent from a game-theoretical perspective.

All it takes is for one world leader to not understand or care about the clear economic negatives to tariffs to start the chain: everyone else can be a rational actor.