Why was there a need to create the ether when we knew the existance of magnetic fields? I have been reading about 19th century physics and how it was believed that electromagnetic waves needed a medium in which they traveled at c, my question is why was it thought that the ether needed to exist and it was respect to this medium that light traveled at c instead of thinking that it was respect to the electromagnetic field
 A: Your question is disjointed. The final sentence makes no sense.
Make sure you know what you're talking about. Classical E&M gives the speed of light in a vacuum as:
$$\sqrt{\frac{1}{\mu_0 \epsilon_0}}$$
Where $\mu_0$ is the permeability of free space and $\epsilon_0$ is the permittivity of free space. Note both of these are constants. Therefore the speed of light is constant as well, regardless of what direction & what speed you're moving in. This doesn't mesh with Galiliean Relativity, which is why aether theory was invented, and why Special Relativity took over after the Michelson-Morley experiment disproved aether theory.
Your suggestion that it could be "with respect to the electromagnetic field" makes no sense, physics wise. You could have written "... instead of thinking that it was respect to the yellow car outside my house right now" and it would actually make more sense, because in physics it's impossible to have a velocity "with respect to a field". See Wiki if you are unsure what a field is.
