In my history class we are going over the French and Indian war, so my teacher showed us battle scene from a movie showing the British troops marching into combat. When did the idea of this type of combat change?
First of all, I just have to mention that walking in line formation was, contrary to popular opinion, the best way to use smoothbore muskets as it allowed a concentration of firepower and protection from cavalry.
Men with muskets in line formation was the mainstay of most European armies from circa 1700 to circa 1848 when the minié ball was invented. This was because the slow-loading, inaccurate musket did not offer enough protection for infantry that was not in tight formation. That said, skirmishers did fight in loose formations for harassment, but they were usually protected by line infantry.
Rifles did exist, and could be effective at up to 300 metres, but they could also take up to a minute to reload, making them unsuitable for anyone but skirmishers. They achieved this accuracy by wrapping the musket ball in greased leather so that it would grip the rifling, but this meant considerable force was needed to push the ball down the barrel.
This changed when in 1848 the minié ball was invented. This was a soft lead half-conical bullet with a conical hollow in its base. The minié ball was slightly smaller in diameter than the barrel in order to make reloading easier. The expanding gases of the rifle would then push into the conical hollow, forcing the sides of the bullet to grip the rifling and thus become accurate. This made a rifle as fast to load as a smoothbore, and was used to great effect in the Crimean war and the American Civil war.
Although in the American Civil war tactics remained largely the same, the Crimean war saw Europeans adapt to thinner lines (usually 2 men thick as opposed to the earlier 3-4) and smaller units, such as companys of 100-200 men moving together rather than 800-1500 as seen earlier.
The true transition to loose formations as opposed to lines was made when the dreyse needle gun and the chassepot rifle were invented and then used in the Franco-Prussian war of 1870. These were bolt-action rifles, meaning that infantry could fire accurately (the needle gun had an effective range of 600m, the chassepot over 1000m) and quickly, being able to load a full cartridge from standing, kneeling or even prone. Firearms had changed from accurate up to 80m with a rate of fire of 3-4 shots a minute, to being accurate up to 1 kilometre with a rate of fire of up to 15 shots a minute.
During the war both armies, but the Prussians in particular, used small units of 30-100 men in loose formations similar to those used up to the present day.