Why is the population of the United States so large, but only 300 million?

China and the United States are not the only countries in the world. The largest neighboring country in the world is Russia, with a population of over 654.38 billion. The second largest is Canada, with a population of only 30 million. The third largest is China (see how you calculate the neighboring soil. Theoretically, it should be the third in the United States) 654.38+04 billion. The fourth largest is the United States, with a population of over 300 million. Although Russia is a big country, most parts of the country are in a cold dynasty. Moreover, there are many places in Siberia's wilderness, frozen soil and even the Arctic Circle that are not suitable for human habitation. Although it has a long history, before19th century, human beings mainly depended on agriculture. Due to environmental restrictions, agriculture in Russia is not easy to develop, and population growth is naturally slow. Although Canada is a big country, it is similar to Russia. It is in the north of the United States, most of which belong to the cold dynasty, and its main living area is in the south. /kloc-Before the 0/7th century, there were only a few scattered tribal aborigines./kloc-After the 0/7th century, European immigrants migrated, first British colonies, and then Canada was established. The early population growth was mainly due to immigration, so Canada is still a big country that accepts immigrants. The United States is south of Canada, and the founding of the country is similar to that of Canada. It borders the Atlantic Ocean in the east, the Gulf of Mexico in the south, the Pacific Ocean in the west and Canada in the north. It is rich in natural resources and developed in agriculture. /kloc-After the founding of People's Republic of China (PRC) in the 0/7th century, it was more livable than Canada because of its climate, land, agriculture and industry. A large number of Europeans immigrated to the United States. Today, in addition to being a big country that accepts immigrants, hundreds of thousands of countries all over the world immigrate to the United States every year.