You know how Garp every now and then used to visit Luffy in Foosha Village. Imagine if one day, he had brought his whole ship and men with him and then encountered Shanks in the town bar. Lol
Considering, Luffy sprouting he wants to be a pirate thanks to Akagami. I think Garp would be angry but not attack full on, just a small fight and argument. But i seriously do think Garp can capture Shanks at that time..remember when Shanks told that bandit trying to harm luffy that "if you want to fight us, at least bring 1 battleship"...
This leads me to believe Garp's fleet was more than enough to take on Shanks and his crew at that time U_U
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What does everyone think?