The City Hall's tech tree is divided into three main modules: [Technology], [Culture], and [Military].
The [Technology] module has the most research projects, ranging from ancient stone tools and ironware to modern gunpowder, artillery, nuclear fusion, and nanotechnology, to name but a few.
The [Culture] module allows for the unlocking of some entertainment buildings, improving the livability of the territory, and fostering the cohesion and cultural confidence of the residents.
The [Military] module is used mainly to counter foreign invaders. It allows for the unlocking of war buildings, the recruitment of armies, and the enhancement of military combat power.
Of course, technology is the foundation of culture and military. Without strong technological support, robust culture and military are impossible. Many of the research projects in the [Culture] and [Military] modules require [Technology] as a prerequisite.