Walkers are bad enough at the best of times - there are vanishingly few situations where they might even be worth having, and even less where a wheeled or tracked vehicle wouldn't be a better bet. If you want to use them in combat, the only word I can think of for them is 'silly' if they make it to the battlefield at all. Have a look at the threads Phil linked for some discussion of why that is, but for the moment the ideas of "ground pressure", "profile" and "recoil management" are good places to start, along with a bit of contemplation of how you stand them up again if they fall over.
It might just barely be possible, using pre-1900 technology, to make a machine that "walks" in the sense that it is supported by legs which can be moved to new positions one at a time. It will be huge, and incredibly slow, and offer nothing I can see in the way of advantages, but it might be possible if anyone is mad (and rich) enough to try.
Now, if you change the idea to what is effectively a set of powered combat armour for an infantryman, it becomes more worthwhile. Unfortunately that requires technology we don't have yet and may not for a long time, and certainly can't be done before 1900.