Hi navi tasan :) .
It is me again, please remember I am not a teacher.
I think the first, though correct, could be enhanced with commas:-Originally Posted by navi tasan
John's capture, while he was fighting in Spain, changed the course of the war.
John's capture when fighting in Spain changed the course of the war. Is incorrect. "John's capture" would not have been fighting.
The third could be made more acceptable by:-
John's murder, whilst fighting in Spain, changed the course of the war.
I hope this helps.