dominate cause

Chemicals are not the dominate cause of cancer in this country.

The fact that the face is so large and dominating causes the viewer to feel almost minuscule in its presence.

Too often the mere outward show of charity has atrophied the kindliness of heart which, from the doer's viewpoint, is the dominating cause in moulding the result.

A W Kammerer had it right when he pointed this out as a dominating cause of the 1930's crash, more so than the destruction of capital in the market crash at the time.