the reason for this is that in this case , "however" is being used as a conjunctive adverb or a adverbial conjunct i.e however is an adverb in this case acting as a conjunction.
As these two are independent clauses( a group of words that contain a subject and verb and delivers a complete thought) written before and after "however". so , however is used to separate two independent clauses with a semicolon before it and a comma after it .
IN SHORT, WE USE A SEMICOLON AND A COMMA WITH "HOWEVER" TO INTRODUCE A NEW INDEPENDENT CLAUSE IN A SENTENCE.
The missionaries left behind a vivid and description of the development of the kingdom which permitted the detailed reconstruction of the daily lives of the people when their civilization was at its peak.
They have gain mastery over weaving, law, and textiles, the Kongo kingdom art form remains even today's one of the famous art forms. they known even how to use and make it use of wood, cloth, terra cotta, and even stones.
