We experimentally study how economic prospects and power shifts affect the risk of conflict through a dynamic power rivalry game. Players decide whether to maintain the status quo or challenge a rival under declining, constant, or growing economic prospects. We find that conflict rates are highest when economic prospects decline and lowest when they improve. A behavioral model incorporating psychological costs and reciprocity can explain these differences. A survey on U.S.-China relations supports the real-world relevance of these findings. Inspired by the Thucydides’s Trap, this study highlights how economic expectations shape conflict dynamics, offering key insights into geopolitical stability.