Garp is an enigmatic figure in One Piece. We don't know much about what he used to do, why none of the marines ever tried to depose him despite him being a direct threat to what they want to achieve, why he can claim he'll hit tenryuubito and go unpunished and the list goes on. All of these mysteries also tie into why Dragon, the most wanted man in the world, Garp's son, is not being held against him.
All of this could be easily explained by his wife being a Celestial Dragon. I think Garp's wife loves him to the point of obsession, much like Hancock does with Luffy which would bring another great similarity between the two. Perhaps all of the higher ups in the marines know for a fact that if Garp wanted to become a Celestial Dragon, he always could due to his relationship with not just a Celestial Dragon, but one of the God's Knights -- a figure with great influence over the whole order.
Now you might be wondering, in what world would Garp marry a Celestial Dragon? Well, in a world where doing so would save a lot of people. I don't think Garp would willingly marry a Celestial Dragon, but given their power and influence, perhaps he did so as a way to save certain people or countries. Given the authority that the God's Knights have over the Celestial Dragons, it is possible that Garp sold himself out to the Celestial Dragons as a way to harbor peace and protect his own people. The price he paid was becoming the government's dog and marrying a Celestial Dragon and having a son, all against his will. It's likely that he was also at God's Valley against his will, protecting the Celestial Dragons as well as his pregnant wife which he ultimately decided was worth saving for the sake of his future son, that he might be able to find his own answers to the power of his birthright.
Dragon was born, name given specifically because he was a Celestial Dragon, to spite Garp, who still to this day refuses to join their ranks. But against all odds, (Probably cause he has Garp's gigachad genes) Dragon clung to his humanity and eventually broke as many slaves as he could free and created the revolutionary army. In the chaos of God's Valley, Dragon saw opportunity and created a force for freedom that would overturn the Celestial Dragon, living up to his father's hopes. He stole the most powerful devil fruit he could get from the tournament and escaped from the island with the slaves while Roger, Garp and The Rocks pirates were fighting. But him running away was unfortunately not part of Garp's plan.
Garp's not exactly a plan guy, I know, but I still think he had a very simple plan put together based on his own beliefs. His plan was to make the marines strong enough that one day they would be able to seek the justice of the world. That's why at every point he tries to train and encourage the marines to take as much power as they can and eventually revolt. When he saw his son Dragon roaming the world and uniting them against the government over the decades, when he saw that time was passing and his power was waning, he simply chose to take a step back and focus only on the future generations, knowing that the world is in better hands and his son Dragon had a far better plan than he would.
All the while, it's very hard for the government to do anything about this. Garp's wife likely still loves him and her son, so she's using her power to protect them. This means the government can scarcely do anything about it, despite most of the Celestial Dragons and government officials trying to capture him at every step. Marines can't hurt Garp cause he can beat all of them anyway AND his wife's a very influential Celestial Dragon. Remember Luffy leaving loguetown? 100 % all of the marines KNOW who dragon is, they can recognize him, even Smoker knew who he was instantly. Not a single one of the marines even tried to shoot at him or were even that disturbed of him being there. If Whitebeard suddenly showed up they'd be shaking in their boots but Dragon just did as he pleased. The very same sort of immunity that Garp possesses when he wants to do something -- the marines just let it happen.
This would also explain why Garp and Dragon can't do anything about the current state of the world. They would be the two figures who know how truly powerful the world government is. Even if the revolutionaries and the marines held hands and went against the world government, they wouldn't be able to win. As such, they're both waiting for another party to join the fight, one who has the wealth, fame and power to even the odds. I'm talking of course about Luffy. Being the King of the Pirates would give him the knowledge, power and wealth to create the final missing link, revive the ancient weapons and go against the world government. This would be the final piece of the puzzle for Dragon and Garp to spring into action.
It's unfortunate then that Garp is MIA, being under Blackbeard's control. Seeing as we got Atlas to show up in Egghead, I think the next thing we're going to see in terms of reveals and actually taking part of the story will be Blackbeard vs Garp's Wife. And that's going to be a hell of a fight. That's when we'll see what Blackbeard's intentions are, his backstory and his ties to the God's Valley incident. And I would say that Blackbeard would even lose that fight, but him having a fighting chance would show why he needed all those devil fruits. We'd see live that the whole of the world government can't take on a God's Knight, by seeing Blackbeard's crew have massive loses, just as we're going to see Figarland in God's Valley.
All of this could be easily explained by his wife being a Celestial Dragon. I think Garp's wife loves him to the point of obsession, much like Hancock does with Luffy which would bring another great similarity between the two. Perhaps all of the higher ups in the marines know for a fact that if Garp wanted to become a Celestial Dragon, he always could due to his relationship with not just a Celestial Dragon, but one of the God's Knights -- a figure with great influence over the whole order.
Now you might be wondering, in what world would Garp marry a Celestial Dragon? Well, in a world where doing so would save a lot of people. I don't think Garp would willingly marry a Celestial Dragon, but given their power and influence, perhaps he did so as a way to save certain people or countries. Given the authority that the God's Knights have over the Celestial Dragons, it is possible that Garp sold himself out to the Celestial Dragons as a way to harbor peace and protect his own people. The price he paid was becoming the government's dog and marrying a Celestial Dragon and having a son, all against his will. It's likely that he was also at God's Valley against his will, protecting the Celestial Dragons as well as his pregnant wife which he ultimately decided was worth saving for the sake of his future son, that he might be able to find his own answers to the power of his birthright.
Dragon was born, name given specifically because he was a Celestial Dragon, to spite Garp, who still to this day refuses to join their ranks. But against all odds, (Probably cause he has Garp's gigachad genes) Dragon clung to his humanity and eventually broke as many slaves as he could free and created the revolutionary army. In the chaos of God's Valley, Dragon saw opportunity and created a force for freedom that would overturn the Celestial Dragon, living up to his father's hopes. He stole the most powerful devil fruit he could get from the tournament and escaped from the island with the slaves while Roger, Garp and The Rocks pirates were fighting. But him running away was unfortunately not part of Garp's plan.
Garp's not exactly a plan guy, I know, but I still think he had a very simple plan put together based on his own beliefs. His plan was to make the marines strong enough that one day they would be able to seek the justice of the world. That's why at every point he tries to train and encourage the marines to take as much power as they can and eventually revolt. When he saw his son Dragon roaming the world and uniting them against the government over the decades, when he saw that time was passing and his power was waning, he simply chose to take a step back and focus only on the future generations, knowing that the world is in better hands and his son Dragon had a far better plan than he would.
All the while, it's very hard for the government to do anything about this. Garp's wife likely still loves him and her son, so she's using her power to protect them. This means the government can scarcely do anything about it, despite most of the Celestial Dragons and government officials trying to capture him at every step. Marines can't hurt Garp cause he can beat all of them anyway AND his wife's a very influential Celestial Dragon. Remember Luffy leaving loguetown? 100 % all of the marines KNOW who dragon is, they can recognize him, even Smoker knew who he was instantly. Not a single one of the marines even tried to shoot at him or were even that disturbed of him being there. If Whitebeard suddenly showed up they'd be shaking in their boots but Dragon just did as he pleased. The very same sort of immunity that Garp possesses when he wants to do something -- the marines just let it happen.
This would also explain why Garp and Dragon can't do anything about the current state of the world. They would be the two figures who know how truly powerful the world government is. Even if the revolutionaries and the marines held hands and went against the world government, they wouldn't be able to win. As such, they're both waiting for another party to join the fight, one who has the wealth, fame and power to even the odds. I'm talking of course about Luffy. Being the King of the Pirates would give him the knowledge, power and wealth to create the final missing link, revive the ancient weapons and go against the world government. This would be the final piece of the puzzle for Dragon and Garp to spring into action.
It's unfortunate then that Garp is MIA, being under Blackbeard's control. Seeing as we got Atlas to show up in Egghead, I think the next thing we're going to see in terms of reveals and actually taking part of the story will be Blackbeard vs Garp's Wife. And that's going to be a hell of a fight. That's when we'll see what Blackbeard's intentions are, his backstory and his ties to the God's Valley incident. And I would say that Blackbeard would even lose that fight, but him having a fighting chance would show why he needed all those devil fruits. We'd see live that the whole of the world government can't take on a God's Knight, by seeing Blackbeard's crew have massive loses, just as we're going to see Figarland in God's Valley.