China has sent 74 warplanes toward Taiwan between late Thursday and early Friday, 61 of which crossed the central line in the Taiwan Strait unofficially dividing the sides.

China's military has called a British warship's recent passage through the Taiwan Strait a disruptive act of "intentional provocation" that "undermines peace and stability". The British Royal Navy says HMS Spey's patrol on Wednesday was part of a long-planned deployment and was in accordance with international law.

If China were to invade Taiwan, no one is certain how different countries would line up. A new paper by the Centre for a New American Security ( CNAS ), a think-tank in Washington, examines that question.