How and why did the Persian kingdom disintegrate?

The Persian state in the 4th century BC was the largest and most powerful state. But in 334 BC, Alexander the Great began a war with the Persians. This was the reason that by 327 BC the lands of Persia were completely captured by the Greco-Macedonian troops. This is how the fall of the largest state in the Ancient East took place. Despite this, already in 323 BC, after the death of the Macedonian king, strife began between his commanders, which led to the split of Alexander’s empire.