The correct answer is deforestation.
Deforestation is the process of clearing a forest in order to make the land useful for a different purpose (like the building of a factory). Teddy Roosevelt, an advocate for conservation of natural resources, saw this deforestation process as a significant problem. This is why he develops the idea of a "Square Deal." This square deal included the idea of conservation of natural resources. This results in Teddy Roosevelet developing the national park services to protect these types of lands.