After a rise in settlement, the western frontier was closed by the year

The settling of people on land in the western regions during 19th century is known as westward expansion. It started with the Louisiana purchase. It was sustained by the Oregon Trail, Manifest Destiny and the Gold rush. There were many westward expansion trails that helped the immigrants and between 1600 and 1870 to expand toward the western regions of USA, three years after the superintendent of the Census announced the western frontier was closed in 1893.  US government also facilitated the migration by passing Homestead acts.

the great wall of china worked as a defense for the feudal states of the zhou dynasty to the north. during the warring states period more walls were put up to defend the borders of the different kingdoms. it was semi successful because despite the wall, the mongols eventually conquered china also the great wall provided protection to the economic development and cultural progress, safeguarded the trading routes such as the silk road, and secured transmission of information and transportation. @jayxboof

crop rotation kepy different plants in the soil instead of once constintly. when switching out plants you have different nutrients being absorbed at different speeds and different roots growing differently therfore the spoil and water flow have to adapt and carry fresh nutrients to carry the constant changes that were going on in the soil.