What caused union membership to soar in the 1930s?

an effect of the steamboat's popularity was that people began building canals in the united states and europe. this was done to find another way to transport goods across the country and in that time, transportation using the river was very slow and dangerous. it depended entirely on manpower and the current of the river. that all changed in the late 1700's when steamboats were introduced. they soon revolutionized travel and trade through the river and dominated the waterways. eventually, other means of transportation took over from the steamboats, but there was a time that they the united states to expand to the west.

answer-the island had airfields that the u.s. military needed.