After running away with the National League Central on their way to a 2016 World Series championship, the Cubs had to fight hard to repeat as division champions last season.
Chicago ultimately pulled away to finish six games ahead of Milwaukee and nine ahead of St. Louis, but if this offseason is any indication, the Brewers and Cardinals could be closing that gap. Both have done so, in large part, by addressing their outfields.
The Cardinals struck first last month, acquiring slugger Marcell Ozuna from the Marlins, but the Brewers fired back with a jarring one-two punch Thursday. After sending four prospects to Miami for all-around star Christian Yelich, Milwaukee soon reached a deal with multi-talented free agent Lorenzo Cain.
The Cubs, meanwhile, have added Tyler Chatwood to their rotation and Brandon Morrow to their bullpen, while Jacob Arrieta remains a free agent and closer Wade Davis signed with the Rockies. Though time remains to upgrade -- and several major free agents are still available -- Chicago has yet to make the same type of splash.

With that in mind, here is a look at how the NL Central challengers have improved heading toward Spring Training:
Brewers
Milwaukee is not standing pat on the heels of its 13-game improvement in 2017, as the club tries to get back to the postseason for the first time since '11. The acquisitions of Yelich and Cain represent huge steps toward ending that drought.
The Brew Crew entered this offseason with breakout pitcher Jimmy Nelson recovering from shoulder surgery, and Trade Deadline acquisitions Neil Walker and Anthony Swarzak free agents. The signings of Jhoulys Chacin, Yovani Gallardo and Boone Logan boosted the pitching depth, but considering some of the question marks on the roster, a bigger splash was required.

Milwaukee made two of those in quick succession Thursday.
The 26-year-old Yelich, who is under affordable club control through 2022, has netted 15.9 FanGraphs wins above replacement (WAR) in his four full big league seasons, thanks to his combination of well above average offense, stellar baserunning and solid outfield defense.
Cain is older -- he turns 32 in April -- and reportedly will make $80 million over the five-year deal. But he too possesses a strong track record of all-around success, with a total of 17.9 WAR since 2014.
By that measure, the Brewers landed two of the nine most valuable outfielders over the past four seasons. And the Steamer projections at FanGraphs have both Yelich (4.0 WAR) and Cain (3.3) ranking among the top 10 outfielders again in 2018.
According to Morosi, the Brewers are expected to play Cain in center field, with Yelich in one corner and either Ryan Braun or Domingo Santana in the other -- with one of the latter two likely to be traded. In other words, Cain is replacing some combination of Keon Broxton, Lewis Brinson (part of the package going to Miami) and Brett Phillips, whom Steamer projected for less than 1 WAR combined in 2018. Yelich supplants Braun or Santana, who both were projected for less than 2 WAR.

Put those gains together and the Brewers improved their outfield by about five projected wins in one day. And Yelich in particular could have room for growth as he leaves Miami for Milwaukee. Of the 240 players who have batted at least 1,500 times since 2013, only nine had a lower home OPS relative to their total OPS than Yelich, who posted a .759 mark at Marlins Park, compared with .800 overall.
Even with those additions, the Brewers may not be done. They still could look to add a front-line starting pitcher -- especially with Nelson's status uncertain -- perhaps using their newfound outfield excess to do just that. But there is no doubt Milwaukee is in much better position than it was a day ago.
Cardinals
St. Louis has finished over the .500 mark in each of the past two seasons, but has not qualified for the postseason in consecutive seasons for the first time since 2007-08 and just the second time since the 1990s.
In response, the club has replaced free-agent starter Lance Lynn with Miles Mikolas and signed Luke Gregerson to help replace a wave of departing relievers. But the most significant turnover has come in the outfield.

First, the Cardinals added Ozuna in exchange for a package of prospects. Next, St. Louis cleared excess outfield depth by dealing Stephen Piscotty to Oakland and Randal Grichuk to Toronto, landing prospects as well as another bullpen arm, Dominic Leone.
Not only does Ozuna's 12.5 WAR since 2014 put him in the top 20 among MLB outfielders -- a bit behind Yelich and Cain -- but he is coming off an impressive breakout campaign at age 26. Ozuna's 142 weighted runs created-plus (wRC) and 4.8 WAR in '17 both put him in the top 10 for outfielders, joining new teammate Tommy Pham.
Looking ahead to next season, Ozuna's Steamer projection (3.6 WAR) fits right in with Yelich and Cain and provides about a two-win bump over Piscotty or Grichuk. Meanwhile, St. Louis' maneuvering also could create more playing time for Jose Martinez, who looks like a strong candidate to continue his own 2017 breakout.
It remains to be seen if the Cardinals will answer the Brewers' splash, perhaps by adding another big arm to the rotation or bullpen, both of which have their share of question marks.
But one thing is for sure as we approach the start of Spring Training -- the NL Central is getting increasingly interesting.