Complex sentence: Political pretext for Slovakian participation in the Polish Campaign was the occupation of small part of Slovakia proper by Poland on December 1 1938, in the aftermath of Munich Agreement (totally 226 km² with 4,280 inhabitants, almost all ethnic Slovaks).
Split into simpler sentences: Political pretext for Slovakian participation in the Polish Campaign was the occupation of small part of Slovakia proper by Poland on December 1 1938. Poland did this in the aftermath of Munich Agreement (totally 226 km² with 4,280 inhabitants, almost all ethnic Slovaks).