How did rats invade?

Rats, particularly the black rat (Rattus rattus) and the brown rat (Rattus norvegicus), invaded new territories primarily through human trade and exploration. They often traveled on ships, infesting cargo and food supplies, which allowed them to spread to ports and coastal cities around the world. Once established, their adaptability to various environments and diets enabled them to thrive in urban and rural areas alike, leading to their widespread presence globally.