For more than two decades, combat aircraft flown by the U.S. and its European allies have pretty much owned the sky. Now, Russia and China are spending lavishly on new weapons that could challenge that superiority, spurring a new arms race.

Some of the hardware, both planes and antiaircraft capabilities, is expected to roll out in the next few years. The upgrades come as Moscow flexes its muscles in hot spots such as Eastern Europe and the Middle East and Beijing does so in the South China Sea—heightening urgency among Western military brass to push for their own, next-generation combat planes.

“The most pressing challenge for the United States Air Force is the rise of peer competitors with advanced military capabilities rivaling our own,” Air Force Chief of Staff Gen. David Goldfein told lawmakers in June, days before being confirmed in the job.

Two months later, the U.S. Air Force certified its new F-35 Joint Strike Fighter. Designed to be hard to detect, the plane is specially built for the sort of limited, precision strikes that have become a hallmark of Western military action since NATO’s bombing campaign in Bosnia in the 1990s.

What is considered the Ferrari of combat jets, the F-22, is still relatively new, first fielded in 2005. Designed to shoot down enemy aircraft while flying as fast as twice the speed of sound, it has more recently evolved into a bomber, too, and can soak up intelligence over enemy territory.

More than three-fourths of the U.S. fleet of jet fighters, however, can be traced back to the 1970s. The Air Force has flown its F-15 since 1975. The widely used F-16 has been operational since 1979, and the U.S. Navy’s F/A-18 was first deployed in 1978.

Those older planes are also the backbone of the air forces of many Asian and European allies, along with newer jets like France’s Rafale and the Eurofighter.

Russia plans to start fielding its first stealth fighter, the T-50, in 2018. The twin-engine plane is designed to be highly maneuverable and equipped with sophisticated electronics to spot enemy aircraft from miles away.

Meanwhile, it has deployed some of its latest combat planes, such as the Su-34 bomber and Su-35 fighter, to Syria. Russia’s Defense Ministry couldn’t be reached for comment.

China has historically relied on Russian designs, many older and some built domestically under license. That is starting to change with the new projects. The country’s air force “is rapidly closing the gap with Western air forces across a broad spectrum of capabilities,” the Pentagon said this year in its annual assessment of the Chinese military.