If North Korea makes good on its threats and attacks South Korea and the U.S., the war that ensues is likely to be very bloody but short — as long as China either stays out of it or sticks to sealing its border with North Korea. China’s actions will have a massive impact on the course that any war with Pyongyang is likely to take.

The United States keeps about 28,000 troops in South Korea. They’re there to act as a trip-wire and deterrent against any North Korean attack. Any serious attack on South Korea would trigger a serious U.S. response.

The South Korean military is about 600,000 strong. Through decades of training and equipment buys, it’s modern and very capable. South Korea’s total population is about 49 million.

The North Korean military is about 1.1 million strong, and is one of the largest military forces on earth in terms of manpower. But it is not one of the best trained, and its supplies are not likely to last for very long. A military that cannot eat cannot long fight, and North Korea has not been able to feed itself for decades. Its military is well fed, for now. A war would force it to burn through men and supplies quickly. North Korea’s total population is about 24 million.

The U.S. contributes more than just boots on the ground. It brings the most modern and lethal air force into any conflict, and the clearest view of the battlefield from our fleet of satellites. The B2 and F22 stealth aircraft can be expected to play a very significant role against North Korea’s layered radar and anti-aircraft defenses. Most of North Korea’s gear is Soviet-made and of that era, but it has been upgraded over the years. It will not be able to keep up with U.S. stealth aircraft. The B2 can drop the MOP, the 30,000 pound Massive Ordnance Penetrator, on North Korea’s dug-in bunkers and artillery positions. The B2 can launch from Guam, Japan, or Diego Garcia or even the continental U.S., and therefore can be based well out of range of any North Korean efforts to strike at it. The F22 can outrun and outshoot anything the North Korean air forces can throw at it. Like the B2, it can attack ground targets, and can remain largely invisible to North Korean anti-air.

A war with North Korea is likely to be bloody in the early going because the North has positioned massive numbers of artillery in the mountains just 35 miles from Seoul, and within range of South Korea’s capital. The North could be expected to unleash those guns on the city of 10 million. But the U.S. could be expected to establish air supremacy quickly. The U.S. could strike anywhere in North Korea by air and offshore ballistic missile, launched from submarines and surface ships. As long as the U.S. brought its full naval strength to bear, from Japan, Hawaii, and around the Pacific, the naval side of the conflict would be a quick kill for the allies. North Korea’s navy simply cannot match the U.S. navy. North Korea’s artillery would probably enjoy a short lifespan, until U.S. forces cave in the mountain tunnels from which they fire. American and South Korean conventional air power would devastate North Korea’s air defense net and then rip up Pyongyang’s military infrastructure. South Korean ground forces would probably spend the opening hours of the war repelling a massive ground invasion from the North, but as the air war shifts to the allies’ favor, would push the North Korean ground forces north of the DMZ as they chewed the Kims’ military to pieces. South Korea would suffer massive civilian casualties in the early hours to days of the war, but the North would probably have its military destroyed and then the North Korean state would be dismantled.