Arc de Triomphe Research Questions

Why is there a gap in between the years that the arc commemorates?  It commemorated the time of Napoleon Bonaparte and the WWI effort, but it completely ignores the segment that connects the two - the colonial era.  Why did France leave out this significant piece of history?  Is it scared that recognizing the full truth will alter the image of France?  What does this show about France?  Because France has changed significantly since these happenings, is L'Arc de Triomphe still a relevant monument that accurately portrays France?