The Northern Plains of India have become a fertile plain due to a combination of various physical features and human activities. Let's dive into the details to understand how this has happened.

Geographical Features
The Northern Plains of India lie between the Himalayas and the Deccan Plateau. This region is formed by three major river systems - the Indus, the Ganges, and the Brahmaputra. The rivers originating from the Himalayas bring a large amount of sedimentary material with them. As a result, the Northern Plains are made up of alluvial soil, which is rich in nutrients and ideal for agriculture.

Human Activities
Over the centuries, humans have played a significant role in making the Northern Plains fertile. They have built irrigation systems, dams, and canals to control the flow of water and distribute it evenly across the fields. This has allowed farmers to grow crops throughout the year, leading to higher yields.

Additionally, farmers have adopted modern agricultural practices, such as the use of high-yielding crop varieties, fertilizers, and pesticides. This has further increased crop production and made the Northern Plains one of the most productive agricultural regions in the world.

Impact on the Economy
The fertile Northern Plains have played a crucial role in the economic development of India. Agriculture is the primary source of livelihood for millions of people in this region. The Northern Plains produce a wide variety of crops, including wheat, rice, sugarcane, cotton, and vegetables. These crops are not only consumed domestically but also exported to other countries, generating significant revenue for the Indian economy.

Conclusion
In conclusion, the Northern Plains of India have become a fertile plain due to a combination of natural and human factors. The region's geographic location and the presence of three major river systems have contributed to the formation of alluvial soil, while human activities such as irrigation and modern agricultural practices have increased crop production. The fertile Northern Plains have played a crucial role in the economic development of India and continue to be a vital agricultural region.

The northern plains has become fertile because the major rivers Ganga, Indus and Bramhaputra has flown from this land . As ,these rivers carried minerals with them it helped the land to convert it into fertile land .Alluvium was the minerals that the rivers carried from deposits of Himalayas .This deposited on northern plains making them fertile.