If the Iraq War was wrong, how can the First World War be regarded as right? As relatives of some killed in Iraq called Tony Blair “the world’s worst terrorist”, political and religious leaders in Ireland and Britain were honouring those who died at the Somme, in a war which has many similarities with Iraq.

While it is acceptable to regard British casualties in Iraq as victims of political deceit, it is considered rather insensitive to say the same about those who died in the First World War. This week’s Orange parades, for example, commemorated those who fought and died at the Somme “for the freedoms we enjoy today”, an interpretation of the Great War which Arlene Foster shares.

Few have challenged that view, even in Ireland, which suggests the First World War was almost a moral crusade. (Although Arlene’s logic suggests that the 1916 Rising was therefore an Irish rebellion against freedom, which would make it pretty unusual.)

So why have the two wars generated conflicting attitudes? Either they are not as comparable as this column suggests, or there is an interesting relationship between politics and history in these islands.

Allowing for changes in domestic and world politics, Iraq and the First World War were remarkably similar in origin, intent, operation and aftermath.

Both wars were fought to enhance Britain’s global role. In 1914, the Empire would continue to rule one quarter of the world’s population. In 2003, post-imperial Britain would piggyback on American muscle to influence a new global economic order.

There was one slight difference in that Iraq was also partly due to Blair’s ego. At a dinner shortly before the war I asked a cabinet minister why Britain was so keen on invasion. The reply was something like, “Tony believes in it.” Some people die for their beliefs. Mr Blair appears to have arranged for others to do it for him.

Both wars were based on unreasonable fear. One used the historical argument that whoever occupied Holland and Belgium could invade Britain. The other was a defence against imaginary weapons of mass destruction. Britain reportedly had over 200 nuclear warheads in 2003. Iraq had none, which suggests that Saddam Hussein probably had a better case for invading Britain, than Tony Blair had for invading Iraq.

In both conflicts the British army was under-equipped and ill-prepared. However, Blair urged his troops into Iraq, just as Lord Kitchener told an ill-informed public that their country needed them. Kitchener was born in Ballylongford, Co Kerry. In one of those wonderful ironies of Irish history, some of those he recruited were probably in the Black and Tans who burned Ballylongford in 1921.

Both wars destroyed the social and economic fabric of the defeated enemy’s state, which gave rise to new and violent threats to world peace: the Nazis in Germany and ISIS in Iraq. Finally, the wars shaped social and economic conditions at home. Social unrest in 1920s Britain laid the basis for the welfare state in the 1940s.The dismantling of that welfare system and deceit over the Iraq War contributed significantly to the Brexit vote.

So if the First World War was Iraq on a grand scale, why is it being so intensively commemorated? In Britain it is about sanitising the Empire and its wars. The suffering and sheer brutality of battles like the Somme are more usually described in terms of sacrifice and honour, rather than futility and betrayal. The only positive aspect of the First World War was some wonderful anti-war poetry, but they tend not to include that sort of thing at military commemorations.

In Ireland, the historical emphasis is on Protestants and Catholics dying alongside each other, without indicating that they were fighting, consciously or otherwise, for an empire which would soon turn its might against Ireland.

Irish Protestants and Catholics also fought side by side in the Spanish civil war, this time against fascism. Tomorrow is the 80th anniversary of the outbreak of that war. Political and religious leaders are unlikely to lay wreaths in memory of the Irish who died in Spain.

You might argue that any similarities between the First World War and Iraq are largely academic. Sadly they are not. Apart from illustrating how British history repeats itself (and how the Irish tend not to notice) the importance of the similarities is that the misplaced acceptance of the First World War’s legitimacy helped Tony Blair to lay the basis for another illegitimate war.

It is important to commemorate all our dead but until the Great War is remembered in terms of victims rather than victory, future prime ministers can use the culture of its commemoration as a basis for new British wars.