1) show of power: As one makes new technology, they would either want to test it out or show the other nations that what they produce is ground-breaking and the best. Usually if it is military technology, you would want to test it out, and with the use of “show of force”, can have people groups submit to your country.
2) Better technology: As technology advances, it usually makes something easier. In the case of imperialism, better military advances meant that they could (once again) have other people submit to you
3) Better transportation: This meant that you could take multiple countries at once, and can prove that you’re country is great by having supplies shipped over long distances to keep your troops up. If in need of more troops, you could send more.
hope this helps