Soldiers, probably Czechoslovak troops serving in the French Army manning a trench on the Western front, c1916-17.
Czechoslovakia didn’t become an independent country until October, 1918.
It did not but a Czechoslovak Legion was formed in France in 1914 and served in the French army, in various formations until 1918. In late 1917 an autonomous Czechoslovak army was established, beginning with the 21st Czechoslovak Rifle Regiment. Another regiment was formed in May 1918 and the two were joined together as the Czechoslovak Brigade which fought as part of the French 123rd Infantry Division.