Mainland Southeast Asia

Mainland Southeast Asia is the continental portion of the Southeast Asian region.

It sits east of the Indian subcontinent and south of mainland China. The region is bounded by the Indian Ocean to the west and the Pacific Ocean to the east. This area includes five sovereign states: Cambodia, Laos, Myanmar, Thailand, and Vietnam. It is distinct from Maritime Southeast Asia, which consists of the various island groups off the coast of the peninsula.

The geography of the Indochinese Peninsula is defined by its unique landforms. The peninsula projects southward from the main Asian continent. Several mountain ranges extend from the Tibetan Plateau in the north. These mountains are interspersed with vast lowlands. These lowlands are primarily drained by three major river systems that flow in a north-south direction. The Irrawaddy River flows through Myanmar. The Chao Phraya River is located in Thailand. The Mekong River is another major system, flowing through Northeastern Thailand, Laos, Cambodia, and Vietnam.

Climate and biology also define the region's boundaries. Most of the area experiences a tropical climate. However, certain areas like Northern Vietnam are subtropical.

Biogeographically, Indochina is part of the Indomalayan realm of tropical Asia. It is bounded on the north by the temperate climates of China and the Tibetan Plateau. To the northwest, it meets the mountainous India-Myanmar border. A significant boundary called the Kangar-Pattani Line bisects the Malay Peninsula near the Malaysia-Thailand border. This line separates the evergreen rain forests of Malesia from the seasonally dry tropical forests of Indochina.

History has provided many names for this territory. Ancient Indian literary sources and Buddhist texts sometimes refer to the area as Suvarṇabhūmi, meaning "land of gold." This name, along with Suvarṇadvīpa, may also refer to insular Southeast Asia. The term "Indochina" emerged in the early nineteenth century. It was likely coined by the Danish-French geographer Conrad Malte-Brun in 1804. The Scottish linguist John Leyden also used the term "Indo-Chinese" in 1808 to describe local inhabitants and languages.

The use of the name "Indochina" has been controversial. Malte-Brun later argued against its use in his Universal Geography. He believed the term overemphasized Chinese influence and suggested "Chin-India" instead. Despite this, the term gained traction and replaced names like "Further India." Later, the name became restricted to the French colony of French Indochina, which included Cambodia, Laos, and Vietnam. Today, scholars and residents more commonly use "Mainland Southeast Asia" to describe the region.

Culture and language in the region reflect deep historical connections. The area has received significant cultural influence from both India and China. Myanmar, Thailand, Laos, and Cambodia show strong Indian cultural influences. In contrast, Vietnam is generally considered part of the Sinosphere, meaning it is part of the Chinese cultural sphere.

Vietnam has also experienced some influence from India. Religion is highly diverse throughout the mainland. Buddhism forms a majority religion in several parts of the region. Other traditions include minor Muslim, Christian, and folk religions.

Linguistically, the region is also unique. The languages of the mainland form what is known as the Mainland Southeast Asia linguistic area. While these languages belong to independent families, they have converged over time. They share many typological similarities, which means they have similar structural characteristics. This contrasts with Maritime Southeast Asia, where the Austronesian languages are spoken. The mainland is instead characterized by Austroasiatic, Tai–Kadai, and Sino-Tibetan languages. These patterns help researchers understand how different groups have interacted across the peninsula over many centuries.