The Nationals began spring training this week carrying the expectations of a World Series contender, an already talented team last season improved by this offseason’s moves. Perhaps the best rotation in baseball added a veteran starter in Dan Haren. One of National League’s most powerful lineups when healthy traded for an everyday leadoff hitter in Denard Span. The solid bullpen added the best closer available in Rafael Soriano. Even by early January, this team’s roster was nearly completely set. Fans, however, will remember that the Nationals are only a few years removed from seasons when Odalis Perez was signed a week before 2008 opening day and was the game’s starter. Or when the Nationals reported to camp in Viera, Fla., and team officials had almost two teams worth of players fighting for 40 spots, many with a realistic chance of earning one. Or even two years ago when the final two spots to be decided on the team in March were down to Roger Bernadina, Alberto Gonzalez, Alex Cora, Matt Stairs and Laynce Nix. This year, the Nationals have doled out only 14 non-roster invitations, their 40-man roster already in good shape. One of the biggest themes of this season’s spring training will be depth. It’ll be a word repeated many times, as it was already a focus this offseason by General Manager Mike Rizzo. It’s a long and arduous season and injuries are bound to happen, much like the rash of them suffered by a handful of starting players last season. And that the Nationals starting rotation suffered no injuries last season is an anomaly. The best way to play for injuries is to build depth throughout the organization, in particular at Class AAA. Fielding a strong team at Syracuse protects against major league injuries.