Fans who saw the MCU-shattering Avengers movie couldn't possibly have caught the explanation, since it isn't explained in the film itself. But while strengthening Drax's connection to Thanos and the plot of Infinity War, the new details may raise a few more questions about the larger continuity of Marvel's Cosmic heroes, villains, and the Nova Corps in general.
As we mentioned above, the first Guardians of the Galaxy movie fills fans in on Drax's tragic backstory almost immediately, with "The Destroyer" explaining that Ronan the Accuser slaughtered his family, fueling his mission of revenge. What they may have missed were the clues as to how they died - which only make sense now that the Infinity War has come and gone.
When holding the knife to Gamora's throat in the first Guardians, Drax described how "Ronan murdered my wife, Hovat, and my daughter, Kamaria. He slaughtered them where they stood. And he laughed!" By the end of the film, Drax would come to realize that Ronan was merely a puppet serving Thanos - meaning it was Thanos whom he needed to kill for revenge.
And in Avengers: Infinity War he sees his chance, when sneaking up on Thanos and The Collector in Knowhere. A moment with a deeper meaning, as explained in the home video commentary by director Joe Russo:
"This is a callback to Drax's history with Thanos here... His planet was treated the same way as Gamora's planet. Drax was put on one side, his family was put on the other.
Nobody knew to look any deeper into the details given of Drax's family's death at the time, since it was assumed that Thanos was just as much of a bloodthirsty conqueror in the MCU as the comics. Marvel had yet to reveal the all-consuming (and completely dumb) plan Thanos has for population control. In hindsight, connecting the dots makes sense, since the films don't give any concrete examples of other reasons he would send Ronan to murder on his behalf. The most logical conclusion is that Ronan the Accuser was, at least for a time, leading Thanos' mission of killing half a planet's population personally.
If The Avengers: Infinity War aims to combine Marvel's many standalone plots as "all leading to this," then retconning or clarifying Drax's tragedy as further proof of Thanos' overall goal, then job done. But for fans who like to read a bit closer, this new wrinkle raises some story issues in terms of continuity - in films already released, and potentially more films to come later.
For starters, it turns Ronan from a Kree also fueled by revenge, and drawn to the power of Thanos into the cruel, malevolent leader of a senseless genocide. So let's hope that his characterization when Ronan returns in the Captain Marvel movie doesn't try to ignore that detail. And secondly, it seems to put more than a decade (and as much as two) between Thanos killing half of Gamora's planet, and doing the same to Drax's. Even for a galaxy, that would presumably draw a LOT of attention. Since you'd hope that a decade-plus campaign of planetary genocide would put Thanos on the Nova Corps' radar.
Some may argue that he was, but Thanos, his Chitauri Army, and Ronan were too fearsome for any cosmic peacekeeping group or military to stand against. Which is a plausible enough excuse to dismiss problems fans may not want to see... even if it retroactively amplifies their threat and level of power, along with the that of the heroes who beat them. Not to mention suggesting it doesn't really matter if Thanos created the hero Nova before Infinity War even started.
Now let's just hope the other Marvel films can expand on the new Infinity War story implications, without contradicting them.
Avengers: Infinity War is available now on Digital HD, and will release on Blu-ray and DVD on August 14th.