The Progressive Era (also highlights women's contributions)
http://www.pbs.org/wgbh/amex/eleanor/peopleevents/pande08.html

American Women Suffrage
http://www.nmwh.org/exhibits/intro.html

Social Studies for Kids : Spanish American War
http://www.socialstudiesforkids.com/subjects/spanishamericanwar.htm

The World of 1898 : The Spanish American War
http://www.loc.gov/rr/hispanic/1898/index.html

World War 1

BBC News : The Great War :80 Years On (British site)
http://news.bbc.co.uk/1/hi/special_report/1998/10/98/world_war_i/197437.stm

Eyewitness to History: World War One
http://www.eyewitnesstohistory.com/w1frm.htm

The Great War Series : WW1 Archives
http://www.wtj.com/wars/greatwar/

The Aerodrome ; Aces and Aircrafts of World War 1 (very detailed site)
http://www.theaerodrome.com/