What makes China an urgent military threat? First, Beijing has made clear it is willing to use force to take Taiwan. Subordinating the island isn’t only about incorporating a putative lost province—it would be a vital step toward establishing Chinese hegemony in Asia. And this isn’t mere talk. The Chinese military has rehearsed amphibious attacks, and commercial satellite imagery shows that China practices large-scale attacks on U.S. forces in the region.

Second, China doesn’t merely have the will to invade Taiwan, it increasingly may have the ability to pull it off. China has spent 25 years building a modern military in large part to bring Taiwan to heel. China now has the largest navy in the world and an enormous and advanced air force, missile arsenal and network of satellites. This isn’t to say China could manage a successful invasion of Taiwan tomorrow—but Beijing could be very close. It will be “fully able” to invade by 2025, Taiwan’s defense minister said recently. China’s military power is improving every month.

Third, China may think its window of opportunity is closing. Many wars have started because one side thought it had a time-limited opening to exploit. Certainly this was a principal factor in the outbreaks of the two world wars. Beijing may reasonably judge this to be the case today.