Recently, the debate about whether US power is declining under the Obama administration in Ukraine, the Middle East and elsewhere, or whether it is rebalancing following expansion during the tenure of president George W. Bush has hit new highs.

But perhaps the key area of debate in the 21st century is Sino-American relations and how a more aggressive or expansionist Chinese policy with its neighbors and the US response is viewed.

In recent years, Beijing has taken a variety of more aggressive actions to back its prior claims in land, air and maritime border disputes with Japan, Taiwan, South Korea, Vietnam and the Philippines.

While each example has case-specific issues, the broader picture is often interpreted as China challenging US primacy in Asia.

Following events can be dizzying on this fault line. This week the US and China have been holding meetings to formulate a code of conduct, including some redlines for preventing military confrontations from escalating and to facilitate communications.

Also, on Tuesday, China sent two aircraft into Taiwanese airspace around the disputed South China Sea that set off fireworks between China and Taiwan.

This was only days after China sent an aircraft to engage a US spy plane conducting surveillance from around 200 km. off China’s coast.

By the US account, the Chinese aircraft came threateningly within approximately 10 meters of the US plane and executed a barrel roll nearby, a maneuver that often is employed in combat.

The US decision to publicize the incident was a partial flexing of muscles as it could have covered-up and dealt with it quietly, but on the flip side it appears the US will not take further action.

China has denied that its aircraft acted improperly and has accused the US of crossing redlines in spying too close to its coast.

In the broader picture, on November 23, 2013, Beijing declared a new, expanded, air defense zone in an East China Sea area where it has several border disputes, though primarily with Japan.

Air defense zones are far broader than a country’s airspace, which is limited to 12 nautical miles (22.2 km.) from a nation’s coastline, but also grants a country fewer rights, mostly only the authority to require foreign aircraft to identify themselves.

Under international law, few specific provisions are cited as a basis for air defense zones, but since the early 1950s, many countries, starting with the US, have established such zones, which many say have at least customary international law recognition at this point.

China’s air defense zone has been considered more controversial because of the context of the areas in dispute, that some of China’s conditions exceed those of other air defense zones and that its actions regarding the zone have been viewed as a precursor to a territory grab (in some disputed areas China has set-up man-made islands, sent in oil-gas exploration ships and engaged in land reclamation activities).

But it has deflected criticism saying that the US started the air defense zone concept, uses it the most and that Japan has expanded its air defense zone unilaterally multiple times.

China’s response to the alleged barrel-roll incident is probably the most indicative: its demand that the US stop spy-flights “close” by (which some have noted as odd for a flight from 200 km. away) regardless of the factual dispute of what occurred.

It says it is merely preventing US expansion of power in Asia as part of the Obama administration’s “Asia pivot” that has included expanded regional missile defense, new and augmented basing arrangements in Australia, Guam and Singapore, recent military exercises and reconnaissance of Chinese territory, the persistence of Cold War–era security alliances and the emerging US military concept of “air-sea battle,” which China claims was made to coerce it with the threat of a decapitating preemptive attack.

The US response has been very mixed, both diplomatically refusing to recognize the new zone and making a point of sending military aircraft through the new air defense zone while instructing commercial flights to voluntarily comply with the zone to reduce tension.

The US’s reactions leave unclear whether it would really (as Barack Obama promised Asian allies in a recent Asian tour) fight for some of the scattered islands in dispute on behalf of its allies, or take another “Ukraine-style” position of mere criticism.

Ultimately, only that kind of test may clarify whether recent incidents were self-contained, or precursors to broader Chinese attempts to increase its influence at the expense of the US.

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