What is the longest river in the world?

The Nile River, which flows through eastern Africa, is generally considered the longest river in the world.  There is some debate, however, on this topic.  Some researchers say that the Amazon is the longest river in the world.
The source of the Nile River is Lake Victoria in Tanzania.  The river flows north for over 4,000 miles through many East African countries.  The country that is usually associated with the Nile River is Egypt.  Ancient Egyptians relied heavily on the Nile River for defense, agriculture, and trade.  The Nile River is still important today for the agriculture of the countries it flows through.
The Amazon River is also over 4,000 miles long. It flows through many countries in South America.  Scientists studying the Amazon River have debated about its source.  Recent studies state that the source of the Amazon River is the Mantaro River in Peru.