Both the ancient Roman empire and the Han dynasty in China were notable for their achievements in technology - the Romans mainly focusing on engineering projects, and the Chinese mainly focusing on science and efficient agriculture.
Lets propose that at the height of both empires (say around 400 AD) the Romans and the Han made contact. They become close allies, freely share their science and technology, and ultimately merge their empires (let's not worry about the specifics of how that merge happens, lets just assume they work it out somehow).
How would the appearance of such a scientific global superpower have impacted the development of mankind from a scientific, industrial, and political perspective?