In the EU, the threat that Palpatine was preparing for (as the theory/my recollection goes) were the Yuuzhan Vong. The Vong absolutely hated technology and especially droids (IIRC; I believe their backstory had their homeworlds and/or entire galaxy destroyed by a race of sentient robots). They made use of highly-advanced, genetically-engineered, living ships, systems, weapons, and armor. For example, one particular engineered being was used to manipulate gravity fields to act as defensive shields on a small scale. When scaled up, those things could manipulate gravity to a point where the Vong could pull moons out of orbit onto the planet below [(which is how they killed Chewbacca in one book)](#spoiler). They also brought massive worldships with them, making their invasion force almost entirely self-sustaining. To make matters worse, the Vong and their "equipment" were all not just almost entirely immune to the Force, but didn't even register in the Force (I recall them being described as "voids" in the Force). The Jedi couldn't sense them, couldn't sense danger from them, and couldn't use Force abilities against them, making the Vong difficult to fight. Individually and collectively, Vong warriors were highly-trained and competent fighters. I think Palpatine found out about them through the Chiss, Grand Admiral Thrawn's people; I seem to remember the Chiss finding or encountering the Vong at some point and when Thrawn joined the Empire, Palpatine found out. Anyway, if the theory holds, it would make sense that Palpatine, having learned of an impending invasion by an overwhelming force of highly-advanced, highly-trained warriors who give no fucks about your Force bullshit, would focus on force of arms rather than "Force". It's been a long time since I read *any* Star Wars EU stuff, so I might have some details wrong.