Brazil, Indonesia, and the Democratic Republic of the Congo are the three nations with the most deforestation. The Amazon, the largest rainforest in the world at 6.9 million square kilometers (2.72 million square miles), is also one of the most biologically diverse ecosystems and is home to around three million species of plants and animals. The Amazon covers nearly 40% of the South American continent. Legal deforestation persists despite efforts to safeguard it, and nearly a third of the world's tropical deforestation takes place in Brazil's Amazon.

Deforestation, another of the largest environmental issues, is primarily caused by agriculture. Land is cleared in order to cultivate commercial crops like sugar cane and palm oil or to raise cattle. Forests help to reduce soil erosion in addition to carbon sequestration because tree roots bind the soil and stop it from running away, which also avoids landslides. 

Sources:

https://earthorg.mystagingwebsite.com/the-biggest-environmental-problems-of-our-lifetime/