Which is the poorest city in the world?

UN has identified the poorest city in the world, Monrovia, the capital of Liberia.

Why is it poor? What is their industry?

The economy of Liberia is extremely underdeveloped, with only $3.222 billion by gross domestic product as of 2019, largely due to the First Liberian Civil War (1989–1996). Liberia itself is one of the poorest and least developed countries in the world, especially according to United Nations.