Since the end of world war ii, the trend in the corporate tax rate has been relative to shifts in the entire economy.

downward

Explanation:

Just after World War II ended, the corporate tax rate was lowered to 38%a little to encourage economic growth.

Then around the 1950s it started to increase as the American economy flourished (corporate tax rate during 1951 was 50%). The American economy's growth rate was extremely high during the 1950s and 1960s, and the corporate tax rate continued to increase until it reached a maximum of 52.8% in 1969.

Then the 1970s came around and recession with them, and the corporate tax rate started to lower to 48%.

During the early 1980s, the economy was still in a very bad shape and the corporate tax rate fell from 46% fro 1980 to 34% for 1990. During the middle years of the Reagan presidency the economy rebounded, but it again fell into recession when president Bush took over.

The 1990s again saw a surge of the American economy, during president Clinton's double term American economy grew a lot, and the corporate tax rate increased by 1%.

Then again another president Bush came and the economy sank again, and the Great Recession happened. The corporate tax rate remained unchanged.

Then came president Obama and the economy rebounded and started growing again, and luckily the growth hasn't stopped yet. President Trump decided to lower the corporate tax rate to 21% starting 2018.

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