Bush wasn't the only world leader who had information leading him to believe that Iraq had chemical weapons. Russia, (The KGB's successor org is very efficient, if not polite), Great Britain, and other intelligence services all had what they though was reliable information that Iraq had WMD's.

That having been said, the WMD issue was only PART of the reason that the invasion occurred. Saddam had many ties with terrorists, (Hamas, Abu Nidal, Islamic Jihad, the militant wings of the PLO, etc) and was funding terrorist attacks. There were also ties with Al Quaeda, as outlined by the 9/11 commission's report. Hussein was repeatedly in violation of the cease fire agreement which ended Desert Storm, was in violation of the UN resolutions which placed sanctions on the country, and was shooting at coalition aircraft on an almost daily basis while they were enforcing the no fly zone. He was also using the UN oil for food program as a way to bribe his way out of sanctions, which is the real bomb contained in the Duelfer report.
The main reasons that Germany and France did not want the US to go into Iraq were the bribery and weapons sales from Iraq, and the debts which Hussein had incurred with those nations. Russia was against the invasion mainly because of the $40 Billion in development contracts which Hussein had signed with Yukos, the russian state oil giant, and illegal weapons sales to Iraq.

The US has been hated or eyed Jealously in the world for over 100 years, with the exception of brief periods of time when the US bailed other countries out of their foreign adventures (WW1 and WW2, Vietnam (You're welcome again, France) and the cold war ). France even bucked US leadership in NATO shortly after the founding of the alliance and was only a marginal participant. The concept of alliances as long term solutions are a fallacy, as they have never been useful over the long term. The US relationship with Great Britain over the last 60 years is the exception rather than the rule.