Putin just visited the Kuril Islands, and Japan is furious.

Russian President Vladimir Putin visited Iturup Island on Thursday, one of the disputed Southern Kuril Islands, known as the Northern Territories in Japan. The visit prompted a formal protest from Tokyo.

But this is about far more than a single presidential visit. At the heart of the dispute is a territorial conflict that has remained unresolved since the end of World War II and has long complicated relations between Russia and Japan.

With negotiations effectively frozen amid the Ukraine conflict and Japan taking a more assertive approach to its defense policy, prospects for a peaceful settlement appear as distant as ever.

And the implications extend beyond Russia and Japan.

As Japan accelerates its military buildup and reshapes its defense strategy, its changing security posture is drawing growing attention across the Asia-Pacific.

Here's a breakdown of the latest flashpoint.