When President Barack Obama arrives in Australia tomorrow to kick off a

When President Barack Obama arrives in Australia tomorrow to kick off a four-day Asia-Pacific visit, he should receive a warm reception from America’s longtime allies in the region.

The U.S. has deepened military ties with Asia in the past year, at once reassuring its partners of its commitment and capitalizing on mutual fears about China’s rise. Both sides face a simple truth: They need each other, possibly more than ever.

In Australia, Obama is expected to announce an agreement to allow an expanded U.S. military presence in the country. Earlier this year, the U.S. disclosed plans to deploy military ships to Singapore. And Malaysia has joined two multination military exercises with the U.S. for the first time.

Such moves, together with frequent visits by senior American officials — Obama will be the first president to join an annual East Asian leaders meeting later this week — have defused fears that America’s defense presence might wane. They also show the region’s growing concern about China’s more aggressive stance in recent years.

Since 2009, China has confronted Southeast Asian countries over rival territorial claims in the South China Sea, refused to condemn North Korea’s apparent sinking of a South Korean naval vessel, and squared off with Japan over claims to a long disputed island group between Okinawa and Taiwan.

China’s defense spending has increased threefold since the 1990s to about $160 billion last year, and its military has recently tested a new stealth jet fighter and launched its first aircraft carrier.

The core of America’s Asian security presence remains South Korea and Japan, which between them host some 80,000 U.S. troops and several U.S. Air Force and Navy bases. Japan is headquarters for the 7th fleet, America’s naval force in the Pacific.

Encouraged by clear signs of U.S. resolve, the Northeast Asian allies have remained firmly on America’s side.