Invasions

Invasions are large-scale incursions into a territory by an opposing force or entity with the objective of control, occupation, or regime change. The term covers military actions as well as non-military contexts, such as ecological or biological invasions, in which a non-native species spreads into new habitats and disrupts local ecosystems.

Military invasions typically involve armed forces crossing borders to seize territory, topple governments, or compel political concessions. Outcomes can include occupation, annexation, or withdrawal. International law upholds state sovereignty and prohibits aggression, but enforcement is uneven and legality is frequently debated. Invasions employ a range of techniques—ground offensives, air power, naval operations, and amphibious landings—and may be followed by occupation administrations or border changes.

Examples range across history: the invasion of Poland in 1939, Allied invasions in World War II such as Normandy in 1944, and more recent actions including the 2003 invasion of Iraq and later regional incursions. Each example has distinct legal, political, and humanitarian implications and often prompts international reactions, sanctions, or coalitions.

Biological or ecological invasions occur when species are introduced to new regions and establish persistent populations. They can outcompete native species, alter habitats, and reduce biodiversity, with economic costs in agriculture, fisheries, and infrastructure. Notable cases include the zebra mussel in North American waterways and the cane toad in Australia. Management emphasizes prevention, early detection, rapid response, and restoration, though outcomes vary.

In all contexts, invasions pose challenges to security, health, and ecosystems. Responses rely on international law, deterrence, surveillance, and coordinated management to reduce harm and restore stability.