Picking up marks in IB History is all about historiography. Your "opinion" doesn't matter...as much. It is your opinion though that drives the essay forward because you decide which academic's opinion is the right one.
One thing you realise in historiography, is that every opinion and account has a basis in some academic's writing. So you can say that Professor X thought that a surge in German nationalism was the fundamental root of WW1, Professor Y believed the economic encirclement of Germany, led the Kaiser to expand relentlessly out of financial fears, Professor Z found that the British-French alliance, and the long-term failure of the French-Russian alliance caused WW1. Then you have to decide in your essay whether Professor X, Y or Z is right, or even, that all three of them are wrong! They can be wrong in your opinion because X failed to account for economics fears, Y of alliance systems driving economic encirclement and Z of nationalistic sentiments enflaming the economy for colonial expansion. Or they could be wrong because all of them failed to account for the fact that it was the race for the remaining colonies that was the root, imperialism at its finest.
That kind of add-on analysis to what they've written is where your opinion comes in.
I.e. Your opinion/thesis in a history essay is not to formulate the causes of WW1 and decide what is right, but to regurgitate what other people have said, and assess and evaluate their opinions; such assessment and evaluation is to be motivated via your own thoughts and ideas on the extent to which
you think they're right or wrong and most importantly (and this is where the analysis comes in)
why do you think so?
If you want more history advice, PM me. I did History HL in May 2010 and got a 7.
One of my greatest achievements in my most favourite subject during the IB.