Episode I
The plot of Episode I is built around events which indeed took place - the blockade of the planet Naboo by the Trade Federation and the following partial occupation of the planet by the TF forces.
According to the film, the conflict arose because of the disputes between the TF and the Naboo government in taxing the transit trade. Already we see the obvious desire of the author to embellish the truth and instead of reality, to present the desired (the sugary image of Naboo).
As it happened, the planet's distance from the Core Worlds and the low level of its technological development made it unprofitable for cargo transfer or organizing a large trading base. Therefore, there was no speaking about "taxes" on the little cargo that did go through Naboo (usually on the way to the Rim Worlds).
No, the conflict between the TF and Naboo had a much more unsightly basis – the poison of the mollusk "gumto – ugna" ("big barrel" - gungan language). Deadly for a human, it was nevertheless a powerful drug for a dozen of other races, including the Hutts. Naboo's proximity to the largest galactic smuggling centers of Tatooine and Nar Shadaa made the manufacture and export of the refined poison ("gugny") a risk-free and most profitable business. The right for the trade were obtained (not for free at all) by the Trade Federation.
But, the idyll didn't last long. The gungans, completely ignored during the signing of contract, were naturally displeased with the use of their waters for the industrial fishing of "big barrel" and demanded their share in the profits. The TF answered with depth charges. The infuriated gungans quickly made contact with smugglers and, having purchased (with the money obtained by their own "gugny" trade) modern weapons (I hope nobody believes that the gungan culture, which was not familiar even with fire could develop force shields and energy bombs on its own), started organizing attacks on the sea factories of the TF, at the same time threatening the government of Naboo with a full scale biological and ecological war against humans.
The government, fully aware of the warlike character of the gungans, their high intellect and their large experience in biological war, saw as the best to listen to their demands and unilaterally broke the contact with traders suggesting to sign a new one – on terms acceptable to the gungans. Naturally, the gungans were to be paid on the expense of TF profits. The latter refused and demanded for the old contract to be maintained. Since no appeal to the Senate was possible, both sides had to resort to military force.