Where does “西洋将棋” come from?

西洋将棋 (Japanese) comes from Japanese 西洋, from Japanese 化, from Middle Chinese 化.

西洋将棋 (Japanese): chess literally, western-style shogi

Definitions

西洋将棋 traces back through two separate lines of ancestry.

Step	Language	Word	Meaning
1	Japanese	西洋	The West, western countries
2	Japanese	化	-ization, -ification; action of making something...
3	Middle Chinese	化	—

Step	Language	Word	Meaning
1	Japanese	将棋	shogi Japanese chess
2	Japanese	将棊	—