By the 1800s, China had become 4. because of internal problems.

By the mid-nineteenth century, China's population reached 450 million or more, more than three times the level in 1500. The inevitable results were land shortages, famine, and an increasingly impoverished rural population. Heavy taxes, inflation, and greedy local officials further worsened the farmer's situation.

temperatures get warmer — and heatwaves are more common. nothing says summer like warm weather. this rise in temperatures is caused by the tilt of the earth's axis. our planet doesn't sit perfectly straight as it spins — it has a slight lean of approximately 23.5 degrees with respect to the sun, called the axial tilt.

explanation: