Why do you think the third step of pure communism that marx predicted has never taken place

It probably hasn't happened because the theory behind Marxism is wrong. A government can't control the economy efficiently enough for it ever to work well enough for communism to be practical. That's why there are almost no communist countries left today.

in 1803 the louisiana purchase took place, doubling the size of the country. by 1840 almost 7 million americans had migrated westward in hopes of securing land and being prosperous. the belief that settlers were destined to expand to the west is often referred to as manifest destiny.

explanation:

because mexico wanted to choose a centralized location