Iraq used chemical weapons in the Iran-Iraq war: https://en.wikipedia.org/wiki/Iraqi_chemical_weapons_program
Israel used white phosphorous till 2013: http://www.bbc.com/news/world-middle-east-22310544
the Soviet Union was accused of using chemical weapons in afghanistan: http://www.paulbogdanor.com/left/afghan/report.pdf
The UN stated that Cuban units used VX as well as Sarin: https://en.wikipedia.org/wiki/Chemical_warfare#Angola
even the vietnamese used chemical weapons: https://en.wikipedia.org/wiki/Vietnamese_border_raids_in_Tha...
None of these examples include the use of chemical weapons in WWII or WWI. During these wars most major european countries used chemical weapons of some kind.
these instances don't excuse their usage, But I don't believe much is gained by pretending the rest of the world is blameless.