The war fought in spain was significant because it:

Indicated that Napoleon could be defeated on the battlefield.

Explanation:

The French armies entered Spanish territory under the supposed reinforcing of presence in Portugal, yet they diverted to Madrid and engaged in a four-year war that they lost.

The armies following Napoleon's orders with opposing Joachim Muram were demoralized with the overall loss and the reputation of the French was contested.

Napoleon had sought cooperation from the Spanish to invade Portugal yet it was denied.

The battle was made with support from the British and the Portuguese who were a major faction against Napoleon's campaign.

After invading Spain, the consecutive defeat at Waterloo came to end any possibility for Napoleon to recover after his return.

With the formal abdication four days later from Waterloo, Paris got a new government and a return to old regimes.

In Spain is called "Guerra de Independencia" or War of Independence, and it also created geopolitical conditions in the Americas for colonies to seek independence taking advantage of Spain's situation correspondently.

explanation: we can only guess at how our actions may be perceived in the future. doing something really big like killing lots of people, saving lots of people, affecting the lives of lots of people is a sure fire way of being remembered in historical records. we can also make a difference in the history records by being a small influence on something bigger, whether that is as a civil servant, scientist or artist.

of course you could argue that we all affect history just as tiny cogs in a   bigger machine.

if you mean how do people influence our opinions of things which have already happened, then simply by writing a book which looks at things form a different perspective and trying to convince people that this perspective is more accurate or truthful. people do it all the time i.e. richard the third was a terrible or was he? plenty would disagree, it's just that their views aren't the most widely known.n:

d. china

good luck

d is the best choice