You've no doubt heard the famous quip, usually attributed to the Vicomte de Mirabeau*: "Other states possess an army; Prussia is an army which possesses a state." As with lots of these epigrams, there's a kernel of truth in there.

I suggest you look at Iron Kingdom by Christopher Clark. From the chapters I've read, he seems to do a pretty nuanced job of exploring and explaining Prussia's military history and culture.

The question of militarism as Prussian state policy (after Frederick the Great) is fairly clear-cut. Per Clark:

In 1786, it was the thirteenth largest European state in population and the tenth largest in area, yet boasted the third largest army. With a population of 5.8 million, Prussia sustained an army of 195,000. In other words, there was a soldier for every twenty-nine subjects. The size of the army, expressed as a percentage of the total population, was thus 3.38 per cent, a figure that compares with the highly militarized states of the Soviet bloc during the Cold War (the figure for the German Democratic Republic in 1980, for example, was 3.9 per cent).

But the question of militarism as a social philosophy is more complex. Clarks adds an important caveat/distinction here:

Yet the percentage figure is somewhat misleading, since only 81,000 of these soldiers were native-born Prussians. Expressed as a percentage of total population this yields a figure of only 1. 42 per cent, which is comparable with the western European states of the late twentieth century (the figure for the German Federal Republic in 1980, for example, was 1.3 per cent). Prussia was thus a highly militarized state (i.e. one in which the military consumed the lion’s share of resources), but not necessarily a highly militarized society. There was no universal conscription. Peacetime training was still short and perfunctory by present-day standards, the social structure of the army still porous.

I tend to think the the orthodox explanation for why Prussia militarised under Frederick the Great is fairly compelling: Brandenburg sits at a precarious geopolitical crossroads in central Europe, wedged between several large power blocs. The heartlands of Prussia and the German states were the battlegrounds of the Seven Years, Thirty Years and Napoleonic wars. Faced with that kind of near-constant existential threat, you can understand why Prussia would arm itself with a strong military.

*As an aside: Clark also suggests that the 'army with a country' quote isn't Mirabeau at all...

It was the size of this army that moved Georg Heinrich Berenhorst, an adjutant to Frederick II during the Seven Years War, to make the memorable observation that ‘the Prussian monarchy is not a country which has an army, but an army which has a country, in which – as it were – it is just stationed.’

I'm going to quote my own answer to that very question from a year ago:

Probably not nearly as much as you think.

Yeah, that's not a good answer. It's difficult to find a perfect answer for such a broad question, since I doubt that even you and me have the same definition of what constiutes a militaristic society. The german people enjoyed many freedoms that a modern observer wouldn't expect in a "militaristic" country, because in the West we tend to equate a politically strong military with oppressive regimes. Amongst many other liberties, the German Empire had a parliament, which made laws, had some say on the budget and did have completely legal opposition parties. And just like in most other countries in the world, the military was subject to the law and the will of the political leadership. It existed in order to defend its king and its people, instead of being a Junta. So if what you had in mind is shaped by the image of the despotic Kaiser or Generalstab being out to conquer all of Europe, then no, that's entirely WW1 propaganda.

But that's not the entire story. Because the prussian (and later the imperial german) military did have quite a lot of power and standing in the state, even in peace time. This military was also exceptionally large and well-funded. There is a famous adage going like this: "Prussia, is not a state with an army, but an army with a state." To understand the reasons for this we have to take a look at the history of Prussia...

The Duchy of Prussia was formed out of territories conquered by the Order of German Knights, often mistranslated as Teutonic Knights. These lands lie outside and to the east of the secular german confederation that called itself the Holy Roman Empire and so the purssians had a lot of opportunity to conquer when the time came. But first we need to look at another part of Germany: Brandenburg. In 1618 the rulers of Prussia died out without an heir and according to a preexisting treaty the Duchy fell to the Hohenzollern dynasty of Brandenburg. Unfortunately, that was also when the Thirty Years War started, which was incredibly destructive in Brandenburg. Both protestant and catholic armies roamed the countryside, pillaging everywhere. This proved to Frederick William of Brandenburg that he needed a strong military of their own, because he obviously couldn't depend on the HRE to defend Brandenburg-Prussia. So from 1643 on he did build up an army with the help of France. (Yes, that's ironic.) One of the important changes he made was that he proffesionalised the military, while most other armies at the time were essentially mercenery bands. Another important change was that he integrated the nobility into the military. Even though this new military didn't manage to achieve much until the war ended in 1648, it had turned the Hohenzollern into a an important force. Over the next 150 years they conquered a lot of territory and continued to grow and improve their army, until finally they became the second-biggest german state behind the Austrian Empire and got the Holy Roman Emperor's approval to call themselves King. But importantly that title was given for Prussia, not Brandenburg, hence the state being known as the Kingdom of Prussia from then on.

Enter Napoleon: when Bonaparte started his attempt to conquer all of continental of Europe, he defeated the Holy Roman Empires' armies, prompting the emperor to abolish the empire. On of the reasons for this was that towards the end of the 18th century the then current prussian king Frederick William II (again: kinda ironic) didn't care all that much for the military and let standards fall. And even after he died, his successor Frederick William III didn't fare much better. The prussian army was defeated in a number of battles in 1806, which was quite a shock to them. Something had to be done, because until then the prussian had seen themselves as invincible. And so, they did do something: they completely reorganised both the military and the state. Amongst the changes were the introduction of short-term conscription (like the french had done with their levee en masse), the Krümpersystem (which made reservists rotate into and out of units at relatively short intervals) and opened up the officer corps to non-nobles. The effect of these reforms was that even after only a few years there was a large number of well-trained reservists available.

Ok, so now we have arrived at what the military's relation to the people would be until 1918: most adult males would serve either in the army or in a reserve unit and many young men saw becoming an officer as a very good career choice. But there were even more important political changes at the highest level. The prussian kings' conduct leading up to and during the Nepoleonic Wars had been appaling, even going so far that the king was practically the only one in Prussia who didn't want to join in the renewed war against France in 1809. So when Napoleon had to retreat from Russia in 1812, the prussian generals simply ignored their king and prepared to fight against the french. Frederick William III had lost all power to stop them, even though they only did what they thought was best for him and the Kingdom. And thus prussian troops were instrumental in defeating Napolean in the Battle of the Nations at Leipzig in 1813 and the Battle of Waterloo in 1815. These successes cemented the position of the military in the prussian state. In 1814 this was formalised in the formation of the Generalstab (general staff), which was tasked with studying, preparing for and conducting war. During WW1 they would eventually sideline the emperor and take almost complete control of the Empire but not earlier, as many people assume. Apart from the repercussions after the failed 1848 revolution, the people didn't really have it worse than in any other european nation. Though much of the Empire's budget was being spend on the Hochseeflotte (High Seas Fleet) from around the start of the 20th century onwards, which shows the sustained pride and importance of the german military even during a long peace.

As I hope to have shown, the military had a very strong and formative position in the Hohenzollern-ruled state even before Prussia was more than a rather unimportant Duchy, simply out of necessity. Since the nobility (and later on many of the best and brightest of the middle class) became part of a well-trained officer corps, there was a significant connection between the military and the "civilian" establishment. Though, let me point out again that this is still more a voluntary "we like shiny boots and thus give more funding to the military" relationship and not "we have to do everything the military says", as you would find in Japan at this time. The German Empire's military was a continuation of that.

Which brings us back to the question: the German Empire wasn't overly "militaristic", especially when we take the norms of the era into account. It was a constitutional monarchy like man[y] of its neighbours. The monarch liked fancy uniforms and big ships. Not that different from most other european countries at the time. If you were to use this as an argument for militaristic prussia, then we would also have to acknowledge the current existance of a militaristic USA. (Luckyly the Reagan era expansion of the US military falls outside the 20 years rule.) Yet despite its massive defense budget and significant jingoism, few people would name america as an especially militaristic country.

From this previous question: http://www.reddit.com/r/AskHistorians/comments/1d9mnf/was_the_german_empire_more_militaristic/ There are additional interesting answers there.