Mediaval europeans, east asians, central asian, middle easterns, musical instruments?

why medieval europe and central asians including western chinese (uyghurs) and middle easts, sharing there musical instruments? while east asians like China, Korea, Mongolia and Japan has little similar but own unique musical instruments?

ex. almost european nations uses violin, guitar and piano. central asians like persia including western chinese uses daf, kemancheh("ghijac" in western chinese) dutar,

middle easterns uses oud and other.

east asian instrument has their own vesion in every country. example, mongolia has it bowed instrument called morin khuur. chinese don't adopted it. instead, they make thier own version erhu and evolved into korean haegum and japanese kokyu. chinese also invented. guzheng with 15-25 strings which did not adopted by any country. but is has korean vesion kayagum which is in 12 string and japanese koto which is in 13 strings. mongolian yatga with 18 string and vietnamese dan thran with 13 strings.

Mediaval europeans, east asians, central asian, middle easterns, musical instruments?palace theatre

Kazakhstan is in Central Asia and has DOMBIRA, how bout that?