In the modern era it is crucial to win wars, if you lose your production science money and culture go down and eventually you’ll enter in a position that you get destroyed or at the brink of losing the game. So in the modern battlefield of the civilization gameplay, what should you do.
First you have to choose the right social policies which give you military advantages second you need a handful of units. So what unit should it be. In my opinion it are tanks and artillery. Although these units are far not the best units in the game they are still quite powerful and cheap to make. So what you can do is build them in mass production and even though you don’t have the most powerful units tanks are agile and quick and artillery have a good range and are powerful against cities.
So if you are in a modern war build these units in mass production and you are the offensive killer machine.