I just finished a book on the beginnings of WWI where the Austrians accused the Serbian government of being directly behind and plotting the assassination of Ferdinand and the Serbians accuse the Austrians of doing it themselves in order to have an excuse to invade Serbia.  Neither assertion was remotely likely, if even sane.

Then the French and Russians accuse the Austrians of plotting to conquer and absorb Serbia, using the assassination as an excuse to invade Serbia whereas the Austrians feel they have to do something and have every right to take actions to protect their southern border, but they just want to send a strong message to Serbia and have no intention of trying to occupy the country, but can't let them off scott free since Serbian behavior shows them delighted at the brutal murder.  They don't know what to do but then the Russians mobilize and Austria decides Russia is using Austria's actions as an excuse to invade and occupy Austria.

I could go on and on about how the British, French, Germans, Italians and of course the ever-suspicious Turks all decide they have to get in the first blow because obviously all their enemies are determined to have a war, so best have the war now rather than latter, even when historical study shows none of the wanted it and a few, including Kaiser Wilhelm, were terrified in private.

Conspiracy theories, in short, are mentally lazy and harmful and almost always, if not always, wrong.