Researching Economics can destroy your economy. Issues with Housing
Reason- when you upgrade your huts to houses, you lose the benefit of the hut. This causes your max pop to crash, which can really wreck your economy fast. In a game where I didn't get to do it until later, I was losing 20 gildar/turn. Having a big city makes this worse.
Suggested fix: make the act of upgrading a housing structure not lose the population benefits of the housing structure. Either that or make the upgrades 1 turn to do.