借刀杀人
Stratagems of Winning · 胜战计When you lack the strength to defeat an enemy, borrow power from a third party. Let others do the fighting while you conserve resources.
During the Three Kingdoms period, Zhou Yu of Wu wanted to eliminate Cao Cao's naval threat but lacked sufficient forces. He used the strategy of having Zhuge Liang's ally Liu Bei provide the forces and intelligence, effectively using another's resources to achieve his own military objectives.
In 2014-2016, Saudi Arabia maintained high oil production to drive down prices, using low-cost production as a "borrowed sword" against high-cost US shale producers. The strategy aimed to let market forces bankrupt competitors without direct confrontation.
Companies often fund startups or legal challenges to fight competitors indirectly. Google funded Mozilla Firefox for years to maintain browser competition against Microsoft's Internet Explorer — using Firefox as the "borrowed sword" to prevent monopoly scrutiny.