China is waging a 'gray zone' campaign to cement power. Here's how it looks.

China considers Taiwan to be a part of its territory and has vowed to take control of the island

- Niharika Mandhana & Camille Bressange

From the choppy waters of the South China Sea and Taiwan Strait to the frozen ridges of the Himalayas, China is pursuing a relentless campaign of expansion, operating in the hazy zone between war and peace to extend its power across Asia.

Beijing carefully calibrates each move with the aim of staying below the threshold of action that could trigger outright conflict. But, step by incremental step, it has pushed deeper into contested areas, exhausting opponents and eroding their strength with a thousand cuts.

Whether it is probes by war planes, maneuvers by coast guard ships or the creeping construction of new civilian settlements, China is constantly pushing boundaries in what security strategists call the "gray zone." It tests the limits of what its opponents consider tolerable behavior, escalating a bit with every new action.

The Wall Street Journal reviewed years of ship-movement data, satellite images, flight-tracking information and other measures of Chinese activity. Taken together, it shows a clear intensification of tactics meant to intimidate rivals and deepen China's control.

South China Sea Nowhere offers a better look at China's gray-zone playbook than the South China Sea, where Beijing has shifted the balance of power bit by bit to become the dominant force.

The waterway is subject to a welter of competing claims, but tensions flow largely from China's assertion that it is entitled to nearly all of the South China Sea. That puts it at odds with half a dozen other governments that also have claims there. It has also created tensions with the U.S., which doesn't want a vital artery of global trade to turn into a Chinese lake.

Beijing has tightened its grip on the South China Sea through a series of steps stretching back more than a decade.