Corruption is a feature in Earth Empires designed to mimic the unintentional $2 billion bug that became one of the essential aspects of Earth 2025 netgaining strategy. In Earth 2025, there was the unintended bug that any cash beyond 2^31 (2,147,483,648) on hand would cause an error which would erase all of the cash a country had on hand, leaving them with $0. Due to the difficulty of remembering this number, Mehul programmed in an artificial limit at exactly $2 billion, at which any cash on hand between $2 billion and $2,147,483,648 would merely cause the country to be reverted to exactly $2 billion cash on hand, rather than losing all of their money. Going from $2 billion to past $2,147,483,648 cash on hand, still would have resulted in a complete loss of money.
This unintended bug, and its sloppy fix from an apathetic Mehul, added the additional strategy aspect of players being forced to use the public market to acquire and then later sell off food, oil, or technology to expand their assets without increasing their military upkeep or going beyond $2 billion cash on hand. This consequence of forcing more market interaction and adding more skill to the game made the $2 billion limit a popular feature, but the unforgiving quality of possibly losing all of your cash at once, made it very annoying at the same time.
Earth Empires has come up with an elegant solution to allowing this mechanic to still be part of the game, while taking away the frustration of accidentally getting too much cash on hand and losing it all. Their solution was to cause cash on hand past the $2 billion amount to decay at the same rate as food, and like food, to only decay upon the use of a turn. Countries can (relatively) safely keep well over $2 billion cash on hand now without risking losing it to the 2 billion bug. They do, however, still run the risk of losing that cash to attacks and spy operations. Unlike food, however, cash cannot be stored on the market to prevent its decay and to protect it from attacks. Cash must be converted to something else, such as food, oil, or technology to protect it from decay and attacks.
Countries that invest in the Resource Decay bonus for about a month can cause not just food decay to be completely eliminated, but corruption to be eliminated as well. This allows them to keep well more than $2 billion cash on hand at once without losing any of it to corruption.