The Seahawks began training camp today with some pretty simple edicts: Build an offensive line, foster better depth and recreate the chemistry that helped them to Super Bowls in 2013 and 2014.

The Seahawks have been one of the best teams in the league the last five years — No. 3 in wins (56) behind New England (62) and Denver (59) — but they have been on a steady decline since winning Super Bowl XLVIII.

After winning 36 games from 2012 to 2014, the Seahawks have won 20 over the past two years. Double-digit wins are always a sign of success, but it has been a disappointment to see the Seahawks fade — from the Patriots’ 1-yard line in XLIX to bad playoff losses the last two years.

This year they have to reverse the trend. There are three keys to doing it:

OFFENSIVE LINE

Everyone knows this has been the biggest single impediment to Seattle’s postseason success the past two years.

In 2015, the interior of Seattle’s line could not come close to handling good defensive fronts such as those of the Rams, Panthers and Vikings. The result: The Hawks barely survived Minnesota in arctic playoff conditions and then got blown out in the first half of their divisional loss to Carolina.

In 2016, Seattle fielded the worst line in the NFL — and the worst it had put together since Russell Wilson arrived in 2012. The result: Wilson suffered three major injuries, the running game went nowhere and Seattle got blown out by Atlanta in the divisional round.

To fix it, John Schneider tried to make better moves than he made in 2016 — hoping Luke Joeckel, Oday Aboushi and Ethan Pocic are upgrades over J’Marcus Webb, Bradley Sowell and Garry Gilliam.

Pete Carroll, meanwhile, thinks that painful learning year will be enough to make Justin Britt, George Fant, Mark Glowinski and Germain Ifedi better.

“I think probably the biggest area that we’re going to see us grow is in offensive line play,” Carroll said in June. “I think you’re going to see a change in the group and an elevation of their awareness based on that one year of experience. Coming back for a sophomore year, things just jump. George will tell you that, Britt will tell you that, Glow will tell you that, Ifedi — they’ll all tell you how much different it looks to them after a year in the bag. So we’re expecting a big jump there and a really competitive camp coming up.”

It can’t be any worse than it was last year, but the coaches still have to decide which five they plan to start, and those guys need to play together. Until that happens, this unit will not be much better than the neophytic 2016 crew.

The Seahawks will play four of the top seven defensive fronts this season: the Texans, Rams, Giants and Eagles. That’s five really tough games for Seattle’s offensive line — with three of them coming in October.

As we have said before, Tom Cable needs to settle on his starting five by the third preseason game and let them play together for big chunks of those final two exhibitions. If he doesn’t, the Hawks won’t have a chance in the opener at Green Bay, where they are typically blown out anyway.

This unit has to make big strides over 2016 if the Hawks are going to have any shot at their second Super Bowl title.

INJURIES/DEPTH

The Seahawks suffered major injuries to more star players last year than they have in any season since Wilson arrived in 2012.

Wilson played most of the season with a sprained knee, sprained ankle and pectoral injury. Michael Bennett missed five games with a knee injury, Kam Chancellor four with a groin injury and Tyler Lockett missed the playoffs after suffering a broken leg in Week 16.

Earl Thomas was probably the biggest loss on defense, missing five games and the postseason with a broken leg. The Hawks also ran through nine tailbacks, as Thomas Rawls and C.J. Prosise struggled to stay healthy.

With the exception of DeShawn Shead, who is recovering from a torn ACL suffered in the playoffs, those guys are all healthy now and should be set for the opener (barring preseason injuries).

But the Hawks know they need to avoid so much attrition in 2017, so they tried to fortify most of those injury spots. They signed solid veteran safety Bradley McDougald to back up Thomas and Chancellor and drafted four defensive backs. They also drafted two defensive linemen and two receivers and signed Eddie Lacy to help fortify the running back spot.

This could be the most competitive camp Carroll has had, with big battles at running back, receiver, both lines and the secondary.

That bodes well for a deep team capable of handling injuries everywhere but at quarterback. But the Hawks need to stay a lot healthier this year if they are going to have a chance to win it all.

ATTITUDE

The Richard Sherman saga is at the forefront of this issue, but the fact is the defense has become disconnected over the past two years — thanks to various personal gripes and injuries.

Chancellor’s holdout splintered this unit in 2015, and the overly combative attitudes of Sherman and Bennett last year added to the problems created by the handful of title-dooming ailments.

Chancellor said it himself after the 36-20 blowout loss to Atlanta: “We didn’t stay together the whole game. We believed, but we didn’t stay together from an attitude standpoint. We got too caught up in things they were doing, and it kind of took away our energy and drained our energy from us.”

The Seahawks are still an elite defense, especially with Thomas and Bennett healthy. But their historic run of four straight years as the No. 1 scoring defense ended in 2016 as they finished third. Since their championship 2013 season, when they gave up 14.4 points per game, they have steadily risen up to the 18.6 of last year. They need to take that number the other direction again. To do it, they need to “stay together.”

They seemed to rediscover some of their lost chemistry during minicamp in June, and the next few weeks will show whether they really have come back together.

If they do that, avoid the major injuries that doomed them last year and put together just an average offensive line, the Hawks can make a run at another title.