from wiki:
“The Seahawks are the only NFL team to switch conferences twice in the post-merger era. The franchise began play in 1976 in the NFC West division but switched conferences with the Buccaneers after one season and joined the AFC West. This realignment was dictated by the league as part of the 1976 expansion plan, so that both expansion teams could play each other twice and every other NFL franchise once during their first two seasons.
In 1983, the Seahawks hired Chuck Knox as head coach. Finishing with a 9–7 record, the Seahawks made their first post-season appearance, defeating the Denver Broncos in the Wild Card Round, and then the Miami Dolphins, before losing in the AFC Championship. The following season, the Seahawks had their best season to date, finishing 12–4. Knox won the NFL Coach of the Year Award.
The Seahawks won their first division title in 1988, but from 1989 to 1998 had poor records and did not play in the post-season. The team almost relocated, and was in bankruptcy for a short period. In 1997, Microsoft co-creator Paul Allen purchased the team, and in 1999 Mike Holmgren was hired as head coach. He would coach for 10 seasons. The Seahawks won their second division title, as well as a wild card berth in the playoffs.
In 2002, the Seahawks returned to the NFC West as part of an NFL realignment plan that gave each conference four balanced divisions of four teams each. This realignment restored the AFC West to its initial post-merger roster of original AFL teams Denver, San Diego, Kansas City, and Oakland.
Again, The NFL’s AFC conference past or present, no matter how aligned, has or never had anything to do with the American Football League, (AFL), at any time. Seattle was never a part of the AFL. Denver, NY Titans, (Became the Jets), Boston Patriots, Buffalo Bills, Houston Oilers, LA Chargers, (Later went to San Diego), Denver Broncos, Oakland Raiders, Dallas Texans, (Went to KC later), were the first teams in the AFL. (The Miami Dolphins were added later). Seattle was never an AFL team, original or otherwise.