Calling United States the "Police of the world" may seen as generous by some critics of United States' foreign polices. These critics instead may refer it as imperialism, "U.S. Global Empire".
United States' foreign policies have brought US troops to 135 countries around the world including Afghanistan and Iraq, which equates to 70% of the world's countries. These deployment range from as low as 1 to as high as 74,796. Although the total number of troops deployed in foreign soil may be lower than the average in the past 50 years, the number of territories that US troops deployed are the highest in 50 years.
The U.S. foreign policies seem to have a need to impose American believes and virtues onto other nations. Take the case of Iraq. Yes, Saddam Hussein may be a tyrant and it harsh towards Iraq's citizens. Who gives the right for the U.S. to intervene. I am not condoning dictatorship or (alleged) genocide, but no foreign government should interfere with the politics of a sovereign nation. That is what the United Nations is for.
In the case of "Osama Bin Laden" and Al Qaeda. The U.S. [government/president] has to understand that they are not fighting an individual who has a following. Bin Laden has successfully made the war against the U.S. into a religious war; a Jihad. Hence, no matter who is the leader of Al Qaeda the war will not end. The only difference along the way is how organize these individuals will be.
With the U.S. existing foreign policies, they had taken their needs to protect "American interests" to the extreme.
I do not have a solution or grand plan to resolve all the conflicts around the world, but as long as there are unequal balance of power and the ability of any one party to have leverage on the situation the conflicts will continue. I wish the respective governments would put more emphasis on local policies instead. May be then we will have "peace on earth".