Complex sentence: Less obvious is what Boleslav wanted to gain with his participation in the war against the oborite Slavic dukes in far north, probably Boleslav wanted to ensure that powerful German neighbors does not interfere him in spreading the Bohemian estates to the east.
Split into simpler sentences: Less obvious is what Boleslav wanted to gain with his participation in the war against the oborite Slavic dukes in far north. Probably, Boleslav wanted to ensure that his powerful German neighbors did not interfere with him in spreading the Bohemian estates to the east.