There are some teams in the NFL that are expected to be much better because they have made dramatic changes -- Peyton Manning to Denver or Mario Williams to Buffalo are the two most obvious ones this year. Often times, though, teams can make a dramatic improvement while doing much less-publicized, dramatic things to improve areas of major concern.

Here’s a look at four units that struggled last year that should be far better this year because of the changes they have made:

Dallas secondary

Dallas had yet another disappointing season last year, and the secondary was a big part of the reason. They were, frankly, not very good. They were particularly weak along the sidelines. That allowed teams to attack them aggressively, it put too much pressure up front, and it limited the ability of the defensive line to apply pressure for fear of allowing big plays down the field. It was a total waste of the blitzing talent of defensive coordinator Rob Ryan to have such a porous secondary.

This year the story should be much different. First, they were aggressive in free agency. They snagged Brandon Carr, a very good shutdown corner, from the Chiefs, and underrated safety Brodney Pool from the Jets. Then they got aggressive at the draft, trading up to the sixth spot to grab corner Morris Claiborne. He was the jewel of the draft for cornerbacks, and he should be ready to play immediately. Those three seriously upgrade the talent and should allow for a much different storyline in Dallas -- one that is far less depressing for the fans, and much tougher on opposing offenses.

Eagles front seven

Philadelphia made a big change in schemes last year, and it just didn’t work up front. In the scheme linebackers line up wide and take on added responsibility. The linebacking corps just didn’t have the talent or the experience to shine, and they frequently let their team down. They couldn’t generate pressure, and they allowed opposing offenses to stay on the field. When you have a guy like Michael Vick on offense, the defense should be trying to get the ball to him as quickly as possible. But they really weren’t.

They have taken big steps to change things this offseason. First, they made the brilliant decision to trade for DeMeco Ryans from the Texans. In him they have a true leader and an outstanding player -- finally one to build around. In the first two rounds of the draft they continued to focus up front. First DT Fletcher Cox went 12th, then Mychal Kendricks, the linebacker from Cal, was a steal at 46th, and DE Vinny Curry was a nice addition at 59th. Now they have much more talent and some desperately-needed depth. That should lead to a much better defense, and much less disappointing results from the team as a result.

St. Louis defensive line

The Rams had the nucleus of a strong defensive line with Chris Long and Robert Quinn. Two guys aren’t enough, though, and they had really struggled at tackle last year. That had really been an issue in a division that can run the ball -- especially because the secondary was ravaged by injuries last year as well. The team made two nice moves in the offseason which, if they can stay healthy, should make a huge difference. First, they grabbed Kendall Langford from the Dolphins. He’s a very nice player who will contribute at a high level right away. Then they drafted Michael Brockers from LSU at 14th overall. Those two bookends significantly elevate the line. The best part is that the unit is now very young, so if they mesh and are effective the Rams could be set for years to come.

San Francisco receivers

I am an Alex Smith fan, but he desperately needs guys to throw to. Vernon Davis is fantastic, but he needs to be one alternative -- not the only good one. The Niners got aggressive this offseason to get Smith the help he needs. None of the additions are sure home runs, but they are all promising. Mario Manningham is wildly-talented and should shine. Randy Moss seems to be a new man, and he’s smart enough to know that this is his last chance. A.J. Jenkins was a nice pick in the draft. Those three should be able to take a lot of pressure off of Michael Crabtree and allow him to finally play like we know he can -- or at least how he could in college. LaMichael James is a running back with nice hands as well -- something the team hasn’t really had. The Niners won’t be the Saints or the Patriots through the air, but they should be much improved, and much more well-rounded and challenging to defend as a result.