What was one of the Abbasid caliphate's major achievements during its
golden age?

the triple alliance. germany and austria-hungary were already allies by 1879 when, worried about a threat from russia, they formed the dual alliance. italy joined the group in 1882. there was a concern about a possible attack from france and the alliance needed powerful friends to defend it.

arianism, proposed by arius in the third century ce, proposed that jesus christ could not be god because god himself is unique and immutable. this would mean that jesus christ was created by god and therefore lesser. this was considered heretical and banned from orthodoxy, but caught on in germanic cultures. developed approximately around 500 bce by gautama buddha in northeastern india, buddhism first spread to central asia and southeast asia after a few centuries.   shortly thereafter it spread into china, korea, and japan. although initially rome's government persecuted early christian communities, the roman emperor constantine tolerated christians and even converted to christianity himself; christianity became the official state religion. the athenian empire and the nabataeans existed before christianity. the hunnic empire, a great enemy to rome, was never christian. the mongol empire had a christian population that was tolerated but was never officially christian.