Taiwan is the immediate thorn in China’s neck. The one issue China is most desperate to resolve because it sees it as unfinished civil war history and a core sovereignty question. Everything else in China’s external security environment is secondary compared to Taiwan but cumulatively those issues steadily increase China’s strategic burden over time.
If you look strictly at the maritime domain, China’s geography is less favorable compared to countries like Japan and India. Japan is naturally shielded by an island chain that stretches across the Pacific forming a layered maritime buffer. India OTOH projects deep into the Indian Ocean with a peninsular shape that gives it natural maritime access and fewer immediate chokepoints on its western and southern flanks.
China’s coastline is exposed and hemmed in by nearby island chains and chokepoints like the First Island Chain (Japan–Taiwan–Philippines arc). This actually limits their easy access to the open Pacific and creates a semi-enclosed maritime environment in its near seas.
To compensate for those shortcomings, it has built artificial islands by filling shallow reefs and turning them into military bases. But this also has a downside. Instead of making things easier for China, it has actually brought more foreign navies into the area especially the US and its allies.
