RIGA, Latvia — Over a thousand Latvians on Saturday commemorated Nazi-allied World War II soldiers while police used force to prevent violence from erupting between participants and ethnic Russians, who are a minority in the country.

Many Latvians consider March 16, or Legionnaires Day, an opportunity to commemorate war veterans, while Russians see it as an attempt to glorify fascism and whitewash a black chapter in Latvia’s history.

Latvia, which gained its independence after World War I, was occupied by the Soviet Union in 1940, then by Nazi Germany a year later, and again by the Soviets in 1944. During the Nazi occupation thousands of Latvians were forcibly conscripted into the Waffen SS divisions, and many Latvians consider them to be heroes who fought for independence from communism.

Some 250,000 Latvians fought alongside either the Germans or the Soviets, with approximately 150,000 eventually dying in battles....