Months after eliminating a popular challenge to its rule in Hong Kong, China is turning to an even higher-stakes target: self-governing Taiwan. The island has been bracing for conflict with China for decades, and in some respects, that battle has now begun.

It's not the final, titanic clash that Taiwan has long feared, with Chinese troops storming the beaches. Instead, the People's Liberation Army, China's two-million-strong military, has launched a form of "gray zone" warfare. In this irregular type of conflict, which stops short of an actual shooting war, the aim is to subdue the foe through exhaustion.

Beijing is conducting waves of threatening forays from the air while ratcheting up existing pressure tactics to erode Taiwan's will to resist, say current and former senior Taiwanese and U.S. military officers. The flights, they say, complement amphibious landing exercises, naval patrols, cyber-attacks and diplomatic isolation.