Which development most contributed to the start of the second industrial revolution in the late 1800s?

A synergy between iron and steel, and railroads and coal developed .

Explanation:

It develop at the beginning of the Second Industrial Revolution. Railroads allowed cheap transportation of materials and products, which in turn led to cheap rails to build more roads. Railroads also benefited from cheap coal for their steam locomotives.

disease was the number one killer of native peoples. they had had little exposure to the diseases of europe. this led to some villages being almost completely wiped out and some tribes destroyed.

answer; i believe the correct answer is benjamin harrison;