As originally published, the entire 7th Sea setting was presented as it was in the year 1668. A couple of years later, this 'update' book was produced advancing the timeline about 18 months... and of course running into the problem that, if your party pulled off enough epic stunts, things might have gone in a radically different direction! Those beginning a campaign have the option of starting their game in 1668 or using this material and starting in late 1669 instead; those with an ongoing game can consider what's in here in relation to what's happened in their game and adjust accordingly. The intention was to publish a series of these updates, advancing the common timeline a year or so at a time, but for various reasons this didn't happen.
OK, so assuming you want to watch history advance around the ears of the party - and it is an excellent way to remind them of the 'reality' of the world in which the game is being played and even let them get embroiled in world-shaking events if they and you want - what's been going on? It's a time of great change and the title is a bit of a give-away: there is a revolution taking place in Montaigne. This is one of the major events to be discussed with an eye to letting the party participate in events, plenty of opportunity here! Chapter 1: The Fallen Sun deals with it in great detail. Pick the point at which you want to get involved, or if the party is busy elsewhere, the news will catch up with them sooner or later.
The background to the revolution involves a downtrodden peasantry ground down by the wars Montaigne is fighting, the backlash from the Emperor when his daughter fails to present him with the heir he was hoping for and the general poverty and oppression from the 'noble' class. The flashpoint came when a peasant soldier, returned from war, killed a noble who was abusing his wife, a lady the soldier had known and loved before he'd enlisted... and was condemned to death for his crime. A riot erupted and... the rest is, or shall become, history. As things spiral downhill, there are plenty of opportunities for you to weave your own plots around events - perhaps the party will influence them, change them, or perhaps they will merely be witnesses to these momentous events as they go about their own affairs. Left to develop, the revolution results in the overthrow of the Emperor and the establishment of a parliament but all is not as rosey as it might be, power corrupts, as they say and not everyone is content with what is going on. This chapter ends with a 'state of the nation' review which allows you to set adventures in Revolutionary Montaigne, and also lays out the involvement of the various secret societies - perhaps characters who are members were involved in these?
Next, Chapter 2: Vodacce and the New Age details the other momentous event of the year: the discovery and opening up of a strange barrier that apparently was the cause of all ships exploring westward never coming home again. There's a whole lot of background detailing the machinations (the Vodaccian Great Game at play, as always) that led to the discovery, and the reactions to it. Just about every nation and society has its own opinion (although they are a bit distracted in Montaigne as you can imagine) and ideas for exploiting the new opportunities. Fundamentally, though, there's somewhere new to explore...
Then, Chapter 3: Elsewhere is a run-through of what has been taking place in the other nations of Théah. No matter where your party's adventures take them, there are events of which you can take advantage, weaving them into your ongoing plots or letting them serve as a backdrop to whatever is going on.
Chapter 4: Adventures and Campaigns is intended for GMs only (assuming that whoever GMs your group's 7th Sea games is but a single person). It contains secrets underlying the recent history that has just been recounted, and possibly the biggest secret of all: what is the 7th Sea anyway? There are notes on creating your own secret society, and a short adventure - 'The Lady's Fate' - to demonstrate how this all works as one is set up during the course of the adventure. There is a fistful of adventure hooks based around the events described in earlier chapters (just in case reading them didn't give you enough ideas). Finally, an appendix provides a wealth of new NPCs.
On picking this up I was a bit dubious, I've never been a fan of a steadily-advancing timeline within a setting. If you are going to do one, however, this is the way to do it! It's detailed yet open-ended, designed with adventure in mind and of course, it's all optional. Pick the bits you want, and write the history of your own version of Théah!