The United Kingdom, Italy, Denmark, Poland, the Czech Republic, Slovakia, Ukraine, Estonia, Latvia, Lithuania, Romania, Bulgaria, Macedonia, Albania and formerly Spain, Portugal, Hungary, the Netherlands, and Moldova. That's 15 (19 if you include former participants.)
Iceland supported but was unable to provide military support, bringing the number to 16 supporting nations.
That just leaves France, Germany, Belgium, Ireland, Luxembourg, Austria, Switzerland, Norway, Sweden, Finland, Belarus, Slovenia, Croatia, Bosnia, Serbia, and Greece. That's 16, excluding Russia. Almost a 50/50 participation rate, something that's not all that bad.