what offically started and ended WWI? and what made the us enter the war?

Answer 1

https://www.google.com/search?rlz=1C2GGGE_enUS379US455&hl=en&source=hp&biw=1366&bih=643&q=wwi+causes+timeline&gbv=2&oq=wwi+causes+&aq=4&aqi=g6g-v4&aql=&gs_sm=c&gs_upl=1305l20042l0l28532l11l11l0l0l0l0l300l1757l0.1.5.1l7l0

https://www.google.com/search?rlz=1C1GGGE_enUS379US379&aq=f&gcx=c&sourceid=chrome&ie=UTF-8&q=us+entry+into+wwi

Read widely and take good notes.