"Two years ago when I signed my last contract we talked a lot about the future and about bringing great players to the club," said Ljungberg. "Despite building the new stadium we wanted to stay top in England and do well in Europe.
"For me that didn't really happen.
"I stayed because I wanted to stay loyal to Arsenal. But when Henry left this summer it felt like the end for me unfortunately.
"I felt like all the unbeaten players (of 2003/04) had left. I wanted to be loyal but I felt like it was the right time.
But Ljungberg also made no doubt of his intentions for a fruitful West Ham career, citing Eggert Magnusson as a key player in his signature for the Hammers.
"I'm coming here because I want to build a great team," said Ljungberg.
"And why I want to join is because of Magnusson. He wants to bring them forward to be top of the country.
"He's willing to go to the transfer market to buy top players and mix them with youth players. West Ham have a great academy.
"He wants to help take the club up and take them to the top in England. It's a big challenge for me."