Major powers’ interests in enhancing their engagement with Southeast Asian states and the main regional organization, ASEAN, are at a historic high and rising. The United States of America and Japan, the established, mature major powers, and India and China, the re-emerging and neighbouring ones, are each increasing their policy interest in Southeast Asia, Southeast Asian states, ASEAN and the larger regional groupings that include Southeast Asian states. Reflecting this, India, in mid-2013, became the last of these four powers to commit to a separate ambassadorial-level diplomatic relationship with ASEAN. This enhancing engagement is due to the perceived growing strategic influence of key Southeast Asian states, particularly Indonesia, and the perceived central position of the region in the rapidly changing Asia-Pacific security order.

It is clear that some of these major power interests in Southeast Asia are competitive, often pitting China against the United States, Japan or India in the search for closer ties and greater influence with regional states. China's early move to sign a preferential trade deal with ASEAN and Japan's (and South Korea's, India's, Australia's and New Zealand's) tit-for-tat response is held up as an example of such competition as is the present competition between the US-led, China-less Trans-Pacific Partnership (TPP) trade deal and the ASEAN-led Regional Comprehensive Economic Partnership favoured by China and India.

Less commented on is the fact that there is growing policy cooperation among these major powers and Southeast Asian states. The establishment from 2009 of Forum, each exercise co-chaired by an ASEAN and non-ASEAN member of the Forum, is but one example. Greater major power interest in Southeast Asia has strengthened ASEAN as well as ASEAN's role in wider Asia-Pacific regionalism and aided Southeast Asian states to enhance their own security, market access and diplomatic influence.

Southeast Asian states, as small and medium-sized powers surrounded by the world's greatest ones, have long worried individually and collectively through ASEAN. As is the lot of small and medium powers, these worries have oscillated sharply between being ignored and abandoned by these major powers and becoming individually or collectively entangled with and constrained by great powers’ regional interests. The growing engagement in Southeast Asia by the world's four largest national economies have brought the latter fears to the fore. This can be seen by the current concerns in Southeast Asia over the regional implications of US-China and to a lesser extent Japan-China competition.