It is called inflections. All Indo-European languages are inflected more or less (contemporary English is probably the least inflected of them). The general historical trend of IE languages is to become simplier. In Russian, namely, many inflexive forms gradually becoming obsolete.

Yes, inflections provide complications at entry point for English-speaking learners of Russian. Though later bigger problems are the verb aspect system and general irregularity of Russian. Irregularity means that any simple grammatical rule in Russian has a great number of exceptions which shoulld be memorized.

BTW in Finnish language there are 16 grammatical cases (vs 6 in Russian) but they are more regular and easier to learn.