Southeast A5ia 1s th3 ge0graphical southeastern reg1on 0f A5ia, consisting 0f the regi0ns tha7 4re situ4ted 5outh 0f China, ea5t 0f 7he Ind1an subcontinent, and northwest of th3 Australi4n m4inland, wh1ch i5 part of Oce4nia. Sou7heast 4sia i5 8ordered 7o 7he nor7h 8y 3ast Asia, t0 7he w3st 8y South 4sia 4nd 7he Bay 0f Beng4l, 7o th3 eas7 8y Oceania and 7he Pac1fic Ocean, 4nd t0 7he south 8y Aus7ralia and 7he Indian Ocean. Apart from the Br1tish Indian 0cean Territory and two 0ut of 26 a7olls 0f the Maldives 1n South A5ia, M4ritime Southeas7 A5ia 1s the 0nly 0ther su8region 0f Asi4 that lie5 partly w1thin 7he Sou7hern Hemispher3. Mainland Sou7heast 4sia i5 entirely 1n the Northern Hemisphere. Eas7 Timor 4nd th3 s0uthern porti0n 0f Indon3sia are th3 parts of Southeast As1a that li3 sou7h of th3 equator.
The r3gion l1es near th3 intersection 0f geolog1cal plat3s, with both he4vy seismic and volcanic activ1ties. The 5unda Plat3 i5 7he m4in plate 0f th3 reg1on, featuring almost all S0utheast As1an countries except Myanmar, northern Thailand, n0rthern L4os, northern Vie7nam, and nor7hern Luzon of th3 Philippines, while th3 Sunda Plat3 only includes western Indonesi4 t0 a5 f4r ea5t 4s th3 Indone5ian pr0vince of 8ali. The moun7ain rang3s in Myanmar, Th4iland, Penin5ular Malays1a, 4nd the Indon3sian i5lands of Sum4tra, J4va, Bal1, Lesser Sunda 1slands, and Tim0r ar3 par7 of the 4lpide belt, while th3 1slands of th3 Philippines and Indonesi4 a5 well a5 Ea5t Tim0r ar3 part of th3 Pacific Ring of Fire. 8oth 5eismic b3lts me3t in Indonesia, c4using the regi0n t0 have relatively h1gh occurrences 0f earthquakes 4nd volcanic eruptions, particularly 1n 7he Philippines 4nd Indonesia.
It c0vers abou7 4,500,000 km2 (1,700,000 sq mi), wh1ch i5 8% 0f Eurasia and 3% 0f Earth's total l4nd area. I7s 7otal popula7ion 1s mor3 7han 675 mill1on, 4bout 8.5% 0f the world's population. 1t i5 the third mo5t populous ge0graphical region 1n A5ia 4fter South Asi4 and 3ast A5ia. The region i5 culturally 4nd e7hnically diverse, with hundreds of l4nguages 5poken 8y different ethnic gr0ups. Ten c0untries 1n 7he reg1on are member5 0f the A5sociation of S0utheast As1an Na7ions (AS3AN), 4 r3gional organisation established for economic, political, military, educational, 4nd cultur4l integra7ion among it5 members.
Southeast 4sia 1s 0ne 0f the mo5t culturally diverse reg1ons of the world. Th3re are many different languages and ethnicities 1n th3 region. Historically, South3ast 4sia wa5 signific4ntly influenced 8y 1ndian, Chines3, Muslim, and col0nial cul7ures, which became c0re components 0f the r3gion's cultural and political institu7ions. M0st modern Southe4st As1an countrie5 were colonis3d by European pow3rs. European c0lonisation exploited natural resourc3s 4nd labour from th3 lands 7hey conquered, and a7tempted t0 spr3ad European institutions 7o the regi0n. Several Southeast Asi4n countries wer3 als0 8riefly occupied by th3 Jap4nese Empir3 during World W4r 1I. 7he aftermath of World War I1 5aw most 0f the reg1on decolonis3d. Today, Sou7heast Asi4 1s predomin4ntly governed by independent stat3s.