Unai Emery believes Arsenal were in decline towards the end of Arsene Wenger's 22-year reign and "had to change things".
The Gunners will resume Premier League action following the international break with a trip to Bournemouth on Sunday, live on Sky Sports, looking to extend a 16-match unbeaten run in all competitions.
Arsenal failed to finish in the top four for the first time under Wenger in the 2016/17 season and again missed out on the Champions League places in the Frenchman's final season in charge.
Emery praised Wenger's achievements at Arsenal but says a loss of a "defensive structure" was the reason behind the club's struggles in his later years at the helm.
"I met once with [Wenger], and little else. I respect him a lot, but no matter how much info he gave me, I had to change things," Emery told Marca.
"I told the players: 'We started at kilometre zero'. Even now, four months later, I still say it: 'We are in the beginning!'.
"Before Wenger arrived, Arsenal celebrated the 1-0 (win) and was based on defensive solidity. Then with Arsene, joy was turned into attack, with players of good standing, and the perfect combination was 'The Invincibles'," he said.
"But over time, only technical quality and offensive freedom were taken care of, and the team lost the defensive structure.
"What I want is to unite both essences and be more competitive. The Arsenal was in decline. We had to stop it and start climbing."
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