By my understanding machine guns, artillery, tanks, and airplanes are seen as inventions that brought about the conditions of WWI. That makes sense to me but what I never hear is any mention of the role of bolt action rifle. From what I know, by the mid-19th century most modern and wealthy armies fielded their soldiers with rifled muskets. They could fire 3 to 4 rounds per minute, and were far more accurate than muskets. As the century progressed single shot breechloading rifles began becoming standard issue. I recently watched the movie "Zulu", and felt like I saw an accurate depiction of their use. I would think a rifle that could accurately fire 10 rounds a minute would be a game changer. But from what I know, cover was rarely used and most fights still occurred in tight or relatively loose formations. In the very late-19th century bolt action rifles were introduced. How did they affect combat? I imagine cover had to be more widely utilized. I really feel like combat should have stagnated after these rifles were standard issue. Also how did cavalry continue to exist in any form.
How did bolt action affect infantry doctrine in the very late 19th century? Not alot. The reason for this is that infantry doctrine changed before that in response to increasingly accurate rifles with higher rates of fire. Breech loaders were used to great effect in both the Austro-Prussian and Franco-Prussian war but it started long before that.
During the American war of independence light infantry companies were detached from their parent company with increasing frequency and even formed into light infantry regiments, a trend that became more and more common in the 19th century. By the very late 19th century the line infantry had effectively fallen out of favour and the distinction between light and heavy regiments was relatively small in terms of battlefield behaviour.
Basically, the kind of changes we would expect to see if the bolt action had been introduced as a direct replacement for the musket never happened because of the gradual increase in accuracy and range that came with rifled muskets, minié balls etc. By the time the bolt action rifles were adopted en masse the shift in tactics had already occurred.
How cavalry continued to exist is another question entirely. The very brief answer is that cavalry was gradually replaced with dragoon regiments which have a distinct advantage in mobility over regular infantry.