The First Opium War is the best example I could find: a small expeditionary force ran circles around a peer country's army for more than a year and crippled it thanks to total naval superiority and qualitatively better artillery and rifles.
The conquest of Aztecs is another example: Spain annihilated a country with twice the population. Though they cheated with bioweapons of course.
Most of the credit for the conquest of the Aztecs should be given to the hundreds of thousands of native soldiers fighting against the Aztecs, not "bioweapons" (which hurt both sides) or Spanish guns.
I cant think of any.