Gita doesn't say that God created the caste system. The four "varnas" are loosely translated as "castes" but that is not quite so. A varna is defined by an individual's occupation. Those who teach are brahmanas, those engaged in ruling the kingdom and protecting people are kshatriyas, those involved in business are vaishyas and those performing jobs like construction, farming etc. are shudras.

It is unfortunate that many consider a "varna" to be the same as "caste". The latter is a degeneration found aplenty in the Indian society whereas the former is simply a way of classifying people based on their occupation.

There is no parallel to the teachings of Gita. In 18 chapters, it covers all aspects of God, universe and individual and also the means of attaining liberation.