Complex sentence: Just over a year later, his career got a decisive turn when he in the spring of 1921 he met Peter Novopaschenny, a former Russian Navy captain of the tsarist Marine and Professor of Applied Tactics.
Split into simpler sentences: Just over a year later, his career took a decisive turn when he met Peter Novopaschenny in the spring of 1921. Novopaschenny was a former Russian Navy captain of the tsarist Marine and professor of Applied Tactics.