Ubisoft and Massive Entertainment have set their sights on promoting The Division 2 ever since the game's announcement, but it may have caused a player spike for the original The Division spanning the entire month of June and still growing.
Player spikes happen in The Division in about the same manner as the do in World of Warcraft - when a big patch or expansion hits, everyone comes pouring in and then the player base slowly dissipates over time until the next big event. Then again, The Division has Global Events every month which bring an influx of players with them, but holds them for just a week, at best.
The month of June proved to be somewhat of an anomaly when it comes to The Division's statistics, as the player count spiked to 9.372 concurrent players on average, with a peak of 20.826 concurrent players. Note however that this info is from Steam Charts only, meaning it doesn't show the actual number of players, especially since many of of them bypassed Steam entirely and bought the game via uPlay.
This spike in player count could be attributed to several factors, with the prime one being The Division 2 hype as well as Shields, which are achievements that let The Division players earn cosmetic rewards and emotes for The Division 2. Another factor are massive promotions all around, such as the Steam Summer Sale and discounts organised by Ubisoft. This led to potential customers being able to purchase the game for $9,99 / £8.39 or $17,99 / £14.99 with season pass.
The third factor is that The Division is now actually a game worth spending time on. Over the course of two years since its release, Massive Entertainment and Ubisoft have been releasing an update after update, each making the game a more enjoyable experience. This, in turn, possibly crushed any doubts that new players may have had from previous bad reviews thanks to The Division troubled release.
Oddly enough, the 300 per cent growth in player count went under many radars, but reddit sleuths were on top of it once again. This info was unveiled by CyclopsFishInMyWater, who posted a related to player growth and drops during The Division's history. For example, the fact that The Division had this many active players only on three occassions - December 2016, December 2017 and June 2018.