Which advance in medical technology has affected the standards of living of the greatest number of people in developed and developing nations?

The development of vaccines.

when world war i broke out across europe in 1914, president woodrow wilson proclaimed the united states would remain neutral, and many americans supported this policy of nonintervention. however, public opinion about neutrality started to change after the sinking of the british ocean liner lusitania by a german u-boat in 1915; almost 2,000 people perished, including 128 americans. along with news of the zimmerman telegram threatening an alliance between germany and mexico, wilson asked congress for a declaration of war against germany. the u.s. officially entered the conflict on april 6, 1917.

for hobos it was a very hard time most hid on the sides of the railroad tracks causing people to get bulls and get them off sometimes causing in fatal death they couldnt get people to give them money because the   people were also in need of money