Contend, fight, battle, war come into comparison when they mean to strive in opposition to someone or something.
Contend, the most general of these words, always implies a desire or an effort to overcome that which is opposed, but it may imply rivalry rather than animosity, the use of argument rather than the exercise of physical strength or skill or the employment of weapons, a nonhuman rather than a human antagonist.
Fight in its earliest and still most common sense implies a struggle involving physical strength or prowess, originally between men with the fists or with weapons and later also between animals.
In extended use (see also RESIST), fight differs from contend not so much in its range of application, for both may imply other than a human adversary, as in its stress on a rigorous effort to achieve one's ends, and in its suggestion of a struggle against odds or great difficulties.
Battle and war are more picturesque or more poetic terms than fight; they are used chiefly in an extended sense, the first to suggest a continuous assailing or attacking of the enemy or other method characteristic of open battle, and the second to suggest the noise, fury, or tumult of war.