BANGKOK (AP) — Sen. Tammy Duckworth, grilling President-elect Donald Trump’s choice for defense secretary over whether he had the “breadth and depth of knowledge” needed to lead international negotiations, asked Pete Hegseth if could name one member of the Association of Southeast Asian Nations, describe what type of agreement the U.S. had with the countries and how many nations were in the bloc.

Hegseth responded at the heated Senate confirmation hearing that he couldn’t tell Duckworth the exact number of ASEAN nations, but that “I know we have allies in South Korea and Japan in AUKUS (a pact between Australia, the United Kingdom and the U.S.) with Australia.”

“None of those three countries are in ASEAN,” responded Duckworth, a Democrat from Illinois. “I suggest you do a little homework.”

What is ASEAN and why is it relevant to the US?

ASEAN is made up of Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, the Philippines, Singapore, Thailand and Vietnam. An 11th country, East Timor, is set to join soon.

Established in 1967, its goal is to promote regional economic and security cooperation, leveraging a combined population of more than 650 million people with a GDP of more than $3 trillion.

Duckworth’s question came after Hegseth had noted the strategic importance of the Indo-Pacific, a region where China’s influence has been rapidly growing and Beijing has become increasingly assertive in pressing territorial claims.

ASEAN members Vietnam, the Philippines, Malaysia and Brunei are locked in maritime disputes with China over its claims of sovereignty over virtually all of the South China Sea, one of the world’s most crucial waterways for shipping. Indonesia has also expressed concern about what it sees as Beijing’s encroachment on its exclusive economic zone.

What does ASEAN have to do with the US secretary of defense?

The U.S. is treaty partners with ASEAN members Thailand and the Philippines, and Washington has sought to harness ASEAN’s regional influence as it seeks to counter Chinese influence and promote what the White House has called “a free and open region that is connected, prosperous, secure and resilient.”

President Joe Biden said ASEAN was “at the heart of my administration’s Indo-Pacific strategy” and hosted a meeting of ASEAN leaders in Washington in 2022.

ASEAN also holds top-level meetings annually, this year in Malaysia, which holds the rotating chair of the group.

Its defense meetings are typically attended by the U.S. defense secretary, and its foreign minister meetings by the U.S. secretary of state. The meetings culminate with an annual summit, which is regularly attended by the sitting U.S. president. Both Biden and Donald Trump have participated.

Why else is ASEAN important?

Despite some members’ territorial conflicts with China, many in the bloc have close relations with Beijing as well, and top-level Chinese officials also attend ASEAN meetings.

The U.S. in 2022 was elevated to the top-level “comprehensive strategic partnership” with ASEAN — a largely symbolic status that put Washington on the same level with China, which was granted the distinction the year before.

ASEAN emphasizes noninterference and personal diplomacy, and its breadth of membership and partnerships makes it uniquely positioned as a forum to address major geopolitical issues.

Beyond China and the U.S., ASEAN has formal relationships with Russia, India, Australia, the European Union, Britain, Japan, South Korea and many others.

It hosts annual “ASEAN Plus Three” meetings with the leaders of China, South Korea and Japan, “ASEAN Plus Six” talks that add in the leaders of Australia, India and New Zealand, and the East Asia summit, which includes the six plus Russia and the United States.

The ASEAN nations are also central to the Regional Comprehensive Economic Partnership, or RCEP, a free trade agreement that was signed in 2020, creating the largest trade bloc in history.

The 10 nations plus China, Japan, South Korea, Australia and New Zealand account for more than 30% of the world’s population and about 30% of global GDP. Conceived at ASEAN’s 2011 summit, the agreement includes commitments on trade in goods and services, investments and other areas.

Several ASEAN countries are also part of the Pacific rim trade pact known as the Comprehensive and Progressive Agreement for Trans-Pacific Partnership, or CPTPP, whose members also include Mexico, Canada, Australia, Britain, Chile, Peru and Japan, and whose economies make up more than 14% of global GDP.