もう決まったことだから

N5 もう mou already / more N1 決 ketsu decision, vote N4 だから dakara therefore, so, that is why

N3 決 ketsu / ki.meru, -gi.me, ki.maru, sa.ku decide, fix, agree upon

N5 〜から kara Indicates cause or reason, equivalent to because or since, connects two clauses explaining reason N5 〜もう mou Indicates recent completion or change, equivalent to already, shows action completed before now N5 〜と to Indicates company, quotation, natural condition, complete list, or direct connection between elements N5 〜も mo Means also, adds another similar item, often replaces particles such as wa ga or o N5 〜か ka Marks a question, alternative, or uncertainty, appears at the sentence end or between options