Will working the legs improve my overall body strength?

I used to only work out my upper body, but however when I get into a fight I notice that my body overall strength is not improving, which is very disappointing and stressful. my point is not only to build up but also to become strong so i started working exercising my lower body and core. Will it boost my overall body strength? Ps: I did boxing for months
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Will working the legs improve my overall body strength?
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