Scenario: ASEAN Civil War

Background
The ASEAN Civil war is a conflict that lasted between April 11, 2100 until August 8, 2150. Altough it was a conflict between members of the same organization, ASEAN didn't dissolved. The war ended in an SAA victory and the SAC are to pay for damages caused by the war and ASEAN won't become stable again until 2170.

Causes
The war was caused by many things. It was mostly because of disputes between the members of the ASEAN itself. The most members involved in one dispute is the South China Sea. It involved five ASEAN members: Indonesia, Malaysia, Brunei, Philippines, and Vietnam. As a result, there are many disputes between members and this makes the organization fragile and could dissolve at any moment.

Pre-War events
On January 11, 2070, East Timor, Papua New Guinea, and Taiwan join ASEAN to keep the organization stable. China did not like the idea although Taiwan is an independent state since 2020. Tensions began to rise between China and Taiwan. Since Papua New Guinea is still a part of the commonwealth realm and India is a member of the Commonwealth of Nations, the British are involved in the events leading up to the war. On January 20, 2085, Indonesia threatens to leave ASEAN if the1 situation keeps getting worse.

The rest of the members take the threat seriously as Indonesia is the biggest and the most powerful of the members. But the situation just keeps getting worse. India became an observer state on August 1, 2090 to prevent the dissolution of the organization. Taiwan soon joins the Commonwealth of Nations, which triggers more anger from China. East Timor also joins the CON.

Belligerents
On June 20, 2097, Indonesia signed an alliance pact with Thailand and the Philippines which will be later known as the Southeast Asian Axis.On December 15, 2097, Malaysia and Cambodia also signed an alliance pact opposing the SAA which will be known as the Southeast Asian Confederation. Laos then joins the SAC. Singapore is trapped between  Indonesia and Malaysia who oppose each other.

After a long discussion, Singapore eventually joins the SAA. Brunei had no choice but to join SAC. Cambodia still hates Vietnam so Vietnam joins SAA. Myanmar joins SAC. Since the rest of the members are a part of the Commonwealth of Nations, no one joins the opposing blocs anymore. The final belligerents are:

Southeast Asian Axis:

Indonesia

Thailand

Vietnam

Philippines

Singapore

Southeast Asian Confederation:

Myanmar

Malaysia

Laos

Cambodia

Brunei

The War
On April 11, 2100, massive bombardments occurred in Southern Thailand. A few minutes later, Troops are seen coming from every direction which encircles Thailand. The SAA knew that this was a SAC attack. Indonesia invades Malaysian Borneo and Brunei and quickly conquers it. But it's too late for Thailand. The SACs next target is Vietnam. Singapore and Indonesia engaged in naval and air battle against Malaysia. Malaysia is quickly overrun and is vulnerable to an invasion. Vietnam manage to repelled the attack and invades Cambodia and Laos but is halted when Burmese troops arrive.

International reaction is mostly positive towards SAA. Many countries put tensions against SAC but doesn't take military actions, not wanting to start a world war. China supports SAA and SAC countries bordering China begins to put troops and weapons on the border.

Singapore and Indonesia invades and easily conquers Peninsular Malaysia but their advance is halted in Southern Thailand after Myanmar and puppet-Thailand's troops arrive. They are retreating from Thailand but still has a foothold in Peninsular Malaysia. Vietnam faces a second attack and some SAC forces breakthrough the lines, splitting the Vietnamese lines. Vietnam surrenders.

The SAA proposed a peace treaty. It stated that the SAA will control maritime southeast asia while SAC controls mainland southeast asia. SAC rejected the treaty. Public views on SAC is getting worse. Even so, SAC continues its advance into Peninsular Malaysia. Singapore is back to square one. With Vietnam and Thailand as a puppet, SAC is feeling confident. Philippines is now vulnerable to an invasion from the west.

Singapore is facing heavy bombardments and is heavily outnumbered. Singapore surrenders. With the world trade route distrupted, a lot of countries knew that something had to be done. Sumatra is invaded from the east. Philippines is invaded from the west. Most of Northeast Sumatra is conquered. Philippines is left with Mindanao. Borneo is invaded from the north. Indonesia is quickly retreating in Borneo. Soon Borneo is under SAC hands.

But then a stalemate occurred because of resistance wars in occupied countries and internal conflicts in SAC countries itself. SAC is forced to withdraw some troops from the battlefield to fight against the rioters. This also resulted in morale depletion in SAC and morale raise in SAA.

It was then that a lot of countries starts giving weapons to the SAA. Indonesia begins advancing in Sumatra and recaptures it. They prepare for an amphibious assault which force SAC to put a lot of troops in the western part of Peninsular Malaysia. Philippines is invading small islands and begins guerrilla war. Instead of invading Peninsular Malaysia, Indonesia invaded Southern Thailand from the west.

This traps the Malaysian troops and SAC troops in Peninsular Malaysia surrenders. SAC troops in Singapore also surrenders. Singapore is freed. Singapore begins to rebuild their military. Indonesia invades Borneo from the south and slowly conquers it. Together they joined up with the Philippines and recaptures the rest of the occupied parts. Indonesia and Philippines prepare an invasion of SAC-occupied Vietnam.

Indonesia and Singapore continues its advance in Thailand and reaches Burma. They engaged in naval battle in the south china sea and cost both sides a lot. SAA eventually won the battle and invades eastern Vietnam and quickly recaptures the country. Thailand is almost completely freed. Vietnam, Indonesia, and the Philippines invades Cambodia and Laos and they surrendered. Thailand is freed. Myanmar surrenders on August 8, 2150.

Aftermath
Ahter the war, SAC countries pay for damages and war crimes. Both blocs dissolved and ASEAN is now stable. The world trade route is now not disrupted. ASEAN became more powerful than ever with the help of the Commonwealth of Nations. China is still putting tensions on ASEAN.