Firing more than 350 rounds in warning off a Russian radar aircraft that twice entered its airspace on Tuesday, South Korea signaled its resolve to Russia, China, and indirectly, also North Korea.

The use of force was proportionate to the Russian action. With two separate incursions into South Korea's airspace, the Russian Air Force showed wanton disregard for Seoul's sovereignty and its rights under international law. Even by Russian standards, this action was extreme. But the context matters.

Operating alongside the Chinese air force, the Russians intended to intimidate South Korea and Japan and aggravate the United States. Fortunately, the South Korean military has sent a rather unmistakable warning that this kind of incident should not reoccur.

The U.S. should welcome this courage. The evolving Chinese-Russian alliance intends to undercut the American-led democratic international order. It requires riposte wherever it figuratively or literally (as in this case) crosses the line.

But the Russians were somewhat stupid here. After all, China will likely be unhappy with the excessive Russian aggression. That's because Beijing wants to limit Seoul's increasing association with the broader U.S. security umbrella in Southeast Asia. But Russia's aggression will only encourage Seoul to do the opposite and double down on U.S. support, especially in air and missile defense capabilities: two areas Beijing is desperate to see Seoul avoid.

South Korea has also sent an indirect message to North Korea. Kim Jong Un, even before taking the leadership reins in Pyongyang, has regarded Seoul as a malleable foe to be corralled by threat and dominated by force. South Korean President Moon Jae-in has sometimes reinforced this perception by supporting appeasement in face of Kim's escalation. But Tuesday's action will force the North Koreans to reassess that understanding.

In short: Well done, South Korea.