Under the old regime in france the burden of taxation fell mostly on the

Commoners

Explanation:

Under the old regime, most of the burden of taxation fell on the commoners. This was the case despite the fact that the commoners had much less wealth, and benefitted very little from taxes. In general, the clergy and the noble classes paid little (or sometimes nothing) towards taxation in the country. This unfair arrangement was one of the leading reasons for the French Revolution.