@guunahgar zhuge liang was Liu Bei's best strategist. He would help him found Shu Han and govern it after Liu Bei's passing. He would be the only thing preventing Shu Han from collapsing to corruption until his death. After he died Shu Han was quickly conquered by the Jin dynasty who would finally unite China and ending decades of war.
Seriously? He is not supposed to be born, the answer itself is in the chapter, MC literally, said it himself.
If you're so oblivious to these kinds of reincarnation stories set in a historical era, butterfly effect. BUTTERFLY EFFECT, BU-TTER-FLY E-FF-ECT. B-U-T-T-E-R-F-L-Y E-F-F-E-C-T.
Seriously, do you really need something slapped in your face explaining it in the manhwa by saying "This is because butterfly effect, Kongming should not be born yet" to even understand something so basic? Go read it again if you're that da** confused.