On the 20th anniversary of the invasion of Iraq, the Guardian's opinion page featured an article titled "The Real Lesson of the Invasion of Iraq," in which Jonathan Friedland outlined that the mistakes, exaggerations and lies that led to the invasion offer fundamental lessons for our present, in the conflict and beyond.

Friedland points out that he spent most of the past week digging into everything related to the US invasion of Iraq in the British media archives, and came out of this immersion and reflection with two basic lessons.

Lesson One: Don't Do Harm or Harm

The arguments made by former British Prime Minister Tony Blair and former US President George W. Bush for the war in Iraq were many, but the basic principle of the issue of military intervention was that it was in the interest of the Iraqi people themselves, who would be freed from the grip of a brutal tyrant. Saddam Hussein's overthrow did take place, but at a hefty cost of about 300,<> people, according to one estimate, most of them Iraqi civilians.

Friedland says the invasion created a vacuum filled with terror and bloodshed. For many Iraqis, the treatment prescribed by the architects of the invasion – US President George W. Bush and British Prime Minister Tony Blair – was worse than the disease. A former senior intelligence officer told him this week: "No matter how horrible the system is, chaos and turmoil are worse."

Lesson Two: When it comes to secret intelligence. Be skeptical

In raising the issue of war, Blair placed great emphasis on the intelligence he saw, which he said proved "undoubtedly" that Saddam possessed weapons of mass destruction. But this turned out, as he famously, that was completely wrong, as there were no weapons of mass destruction. Chilcot's investigation into the invasion of Iraq concluded that the then prime minister had deliberately exaggerated the threat, a fact alone that would be cursed by history.

He concluded his article with another lesson that he sees as applicable outside wartime: that even the closest allies should never offer comprehensive support to each other, and they should have the ability to discern, supporting a friend when he is right, while retaining the right to back down when he is determined to make a mistake.