While there were many aristocratic cultural influences on Early Modern warfare, we need to be careful about attributing everything about the period to the 'gentlemanly' character of the officer corps.

A key example is the nature of pitched battle. In this period, there's a lot of writing about 'offering battle'. What this means is that you draw up your army in battle formation outside your camp and await your enemy's attack, generally on favorable ground. Your enemy can either 'accept', and advance on you, or refuse, and remain encamped on ground favorable to them, or retreat. If they don't 'accept,' there's really not a lot you can do about it. Generally speaking, they can spot you and get out or deploy into battle formation faster than you can cross the divide between you in battle formation. If they could, though, 18th century generals would try to attack their enemies before they were fully deployed.

This was something emphatically not unique to the Early Modern Period. Before the organization of armies into multiple, semi-independent combined arms formations in the Napoleonic period, which could march along parallel routes and converge on their enemy, it was very hard to make an enemy fight a battle he did not want to fight.

From the wars of the ancient Greeks and Romans, through the Middle Ages, to the Early Modern period, you have a few basic commonalities. Armies were generally assembled to have a mixture of troop types, allowing them to play to their enemies' strengths and weaknesses. Once concentrated, the army marched as a single body along a single route. Because they don't actually take up much space [you could encamp about 120,000 men in a space the size of NY Central Park], it's hard for the enemy to block off many routes available to you, so you have a lot of freedom of maneuver.

Armies marched from dawn to about noon, whereupon they rested and made camp. Generally, they established these camps in good, defensible positions; attacking the army in camp was a formidable task, and one not lightly undertaken without considerable numerical superiority.

The thing about battles is that the things that make one side want to fight them (superior numbers, good defensive positions) tend to be the same things that make their enemies not want to fight a battle, though there are lots of other reasons not to want to fight a general engagement. For one, they're extremely risky; there's much more room for freak chance in battles than in raids, skirmishes, or sieges, and the consequences of failure are even more dire, risking the total destruction of the army. Moreover, beyond the question of risk, heavy losses even among the winners are almost certain, and the results are often barren. Since armies in this period don't have 'fronts' the way we're used to, being able to deploy in battle formation to meet an attack from any direction, large outflanking movements are difficult to pull off, which makes decisive results that much more rare. An army might decide they must fight a battle if something precious to the state, such as the capital or the interior of the country more generally, is being directly threatened, but this is rare, for reasons I'll outline later.

Now, then, let's discuss what does make warfare in the Early Modern Period unique. While pitched battles were comparatively rare in earlier periods, you could argue that, at least compared to the wars of Antiquity, Early Modern generals were comparatively battle-shy. Because of the established balance of power mechanism in Early Modern Europe, military objectives were generally limited; acquiring a slice of territory on the border is a good example. Pressing further risked turning the rest of Europe against you, as you presented a common threat.

As such, 18th century wars generally concerned the control of territory, which depended more than anything on fortresses. Speaking in the broadest generalities, this was the end; more than anything, you wanted to successfully reduce the key fortresses of the territory you seek to occupy. To do this, you might have to defeat the field army defending them, but if you could achieve your goals without resorting to this, so much the better. Siege warfare reached its apogee in this period; fortresses were constructed according to scientific mathematical principles, while armies become equally proficient at reducing them given enough time. With forty days and a good supply of food and powder, a general could feel confident in being able to capture most fortresses. These sieges were grand spectacles, proceeding along exacting lines in discrete steps, which held great cultural appeal in the age of Enlightenment.

18th Century armies also tended to rely more on true supply lines, rather than taking their supplies from the territory they're campaigning through; when most of the available routes into the interior of the enemy country are controlled by strong fortresses, threatening i.e. their capital is very difficult, so trying to draw the enemy into battle that way was not often an option.

In tactical terms, there were strong incentives against taking too-risky options and deploying for battle without the odds strongly in your favor. Muzzleloading firearms require great proficiency from the user, and soldiers were required to learn complex tactical evolutions to be effective in combat. As such, forming good soldiers took a lot of time, and you know the saying, time is money. This was the age of professional armies, as centralized states increasingly took up the burden of feeding, clothing, housing, and training soldiers. Moreover, as the age of absolutism, the coffers of the state and the king were often interchangeable; rulers had a personal interest in managing their state's investment in the soldier. Unnecessary losses in battle represented wasting the king's money; since they also usually named the commanders, we shouldn't be surprised that cautious, battle-shy generals are common in the high command.

To wrap this up, while aristocratic values did influence how war was waged in Early Modern Europe, battles were not the result of gentlemanly agreements, but were calculated gambles and mind games played by commanders, seeking to maneuver to the best advantage to achieve their ends.