Would you kindly explain the exact meaning of 'in the 1900s'?.
The 1900s (the nineteen hundreds) means the decade (10 year period) from 1900 to 1909.
Therefore 'in the 1900s' means the event happened at some point between 1900 and 1909.
We can use similar expressions for every decade:
1950s (nineteen fifties): from 1950 to 1959
1960s (nineteen sixties): from 1960 to 1969
1970s (nineteen seventies): from 1970 to 1979
Hope this helps