The phrase "original impetus" refers to the initial motivation or push behind something. It represents the original reason or force that drives an action or decision. Full definition
At the same time, underlying shifts in the economy have again shifted the interest group politics — these days, manufacturing workers are a small share of overall US union membership, so the original impetus for the Democratic tilt against trade is going away. (vox.com)
Humanitarian ideals existed in classic culture, but the humanitarianism we prize in the West owes most of its original impetus to the gospel. (religion-online.org)
God's existence was required to explain motion's original impetus and prevent certain irregularities from devolving into chaos. (faith.org.uk)