Original: This wasn’t restricted to World War One, for the city had been developing and supplying arms and armour plate for over a half a century before.
Simplified: This wasn’t restricted to World War One, because the city had been developing and selling arms and armour plate for over a half a century before.
Simplified: This wasn’t limited to World War One, for the city had been making and supplying arms and armour plate for over a 50 years before
Simplified: This wasn’t restricted to World War One, for the city was developing and supplying arms and armour plate for over a half a century before.