The duo managed to keep the Hammers in the top flight but were still dismissed in May 2010 by new owners David Sullivan and David Gold, to be replaced by Avram Grant.
But Clarke is philosophical about being axed and insists the credit crunch was a big factor in why he and Zola lost their jobs.
Clarke said: "The new owners came in and assessed what they thought they had to do at the club. They made that decision and that's the owners' job.
"They have to decide what is the best way forward for their club, and that's what Mr Sullivan and Mr Gold did at the time.
"What happened the next season is ifs and buts. If you look at it, though, we didn't make any progress.
"The year before we'd finished in the top 10. The second season was a lot more difficult but there were a lot of extenuating circumstances at West Ham."
Clarke added: "When I first went into that job it was on the promise that we'd always have money to spend in the transfer windows and we were going to push on into the top six.
"But within a fortnight of being in the club, the credit crunch collapse happened. The then Icelandic owner Bjorgolfur Gudmundsson's bank went bust.
"The circumstances changed completely. There was a gradual erosion of the squad and it was an achievement just to keep West Ham in the Premier League that year."
