The 30 years war
One of the biggest tragedies on the european continent ever since, was the 30 years war. Although the name provides the assumption of one single war going over 30 years, there were rather 4 different wars or phases.
Although the main reason for the conflict was the differences betwen catholic and protestant communities, the war was equally about the power and land posessions in Europe. There was already a lot of conflict potential between both religious parties, which had the effect that not much was necessary to escalate the situation.
I think a good overview is given in the Wikiepedia article:
https://en.wikipedia.org/wiki/Thirty_Years%27_War
The Spanish Troops in the Netherlands
From the 2nd half of the XVIth century to the end of the XVIIth century.
As for the main conditions concerning the enlistment of the Spanish tercios, no one could recruit troops without the King's permission. The king or his captains-general authorised the designation of the people chosen by the captain of the recruiting force as "teniente" (lieutenant) and "alferez" (ensign) of the regiment. The subordinate officers (sergeants) were designated by the fieldmaster (mestre de camp) of the tercio. To recruit men for the tercios, public recruitment markets existed in Spain, where the price of the engagements was discussed between the recruiter and the future soldier, down to particles of "reals" and "maravedis".
The Spaniards that Philip II used for his foreign wars never numbered more than 10,000 men, which was the manpower of the 4 Spanish tercios that took part in said campaigns.
The staff of a tercio was composed as follows: A "Maestre del campo" (field marshal), who had a guard of 8 halberdiers around him. Eleven captains, twelve alfereces or ensigns, some "cabo de escuadras" (escuade chiefs), a sergeant-major, a military auditor; a barrachel or field judge who had 4 mounted men at his disposal, a fourrier-maior, a doctor, a surgeon, two alguazils, two secretaries, two executioners.
At the time of the formation of the tercios, the use of the different weapons was also standardised. As a bare weapon for the foot people, the pike predominated. The pertisan and the halberd are the weapons of the commanders, sergeants and officers. The gineta, or short lance, was reserved for the captains. The halberd was the distinctive mark of the tenientes, the alfereces and the sergeants.
In each company there were pikemen and arquebusiers mixed together, but in a certain numerical proportion. If the ensign numbered 120 men, it consisted of 80 pikemen and 40 arquebusiers. These covered the front and the corners of the square formed by the pikemen; they were called the "guarniçion".
All these soldiers had to wear the costume of their home country, short trousers, field shoes or field boots, a leather or iron armour (corselet), on the head your iron helmet called "morion". The sword they carried was more or less large, according to personal discretion and taste. The pikemen wore a small round shield, the "rondache", on their left arm for protection.
The arquebusiers were given as much powder as they could carry in their powder horn, which was worn on the right side of their belt. The bullets were not made in advance either. Each arquebusier received a certain quantity of lead or tin from which he had to cast his bullets. As soon as there was irregularity in the process, this inevitably resulted in irregularity in the shooting, the line of fire of the bullets was not always well calculated, and the calibres were not always adapted to the arquebuses.
The use of the musket was ordered by the Duke of Alba. As it was longer and heavier than the arquebus, the operator had to place the muzzle on a kind of fork pierced into the ground.
The Italian infantry had organised its ensigns in a similar way to the Spanish. The colonel, or field master, commanded the regiment and its first company. Each company counted a captain, an alferez, a sergeant, ten escuade chiefs, two drummers and a piper. The regimental staff grouped the colonel, the sergeant-major, the fourrier-major and the barrachel (military court officer in the field). The ensign usually numbered 200 men, without, as I said, this number not being subject to certain fluctuations. For example, under the Duke of Alba, an Italian coronelie consisted of 4000 men divided into 16 ensigns, i.e. 250 men per company.
The main mercenary types in the 30 Years War
The Pikeman
The pikeman is the lowest-ranking unit, but nevertheless very respected at the beginning of the war and well payed at the beginning of the war. This is most likely because the pikeman was at the head of the front. Most of the pikemen were new, young men who had hardly any combat experience. They learned how to fight from scratch. The German phrase "Von der Pike auf" describes this well.
Because the pikeman stood directly at the front, he was usually given a suit of armour (at least at the beginning of the 30 Years War). The surviving originals of pikemen's armour show that the quality was rather inferior. Most pikemen also wore a helmet, like a Morion or Cabasset. The Morion was a rather old fashioned type of helmet, more common in the 16th century, mostly related to the spanish "Conquistatores". The Cabasset is more standard in early to mid 17th century.
The pike was the pikeman's main weapon and was mainly used to defend cavalry. It had a diameter of 3 to 6 cm and was up to 6 m long with an iron tip.
As a sidearm they carried either a rapier or a shorter sword. The sword was very popular with the pikemen because it was shorter and therefore did not interfere so much in the tight tercio. In the course of the war, the pikeman lost his status and there were fewer of them. The musketeer took over because it was more flexible.
Musketeer / Arquebusier
The term musketeer comes, of course, from the musket, the main weapon of this type of mercenary. The same applies to the arquebusier. Along with the pikeman, they make up the bulk of a tercio. While the pikeman protects the musketeer/arquebusier from the cavalry, the latter fires his shot on command and retreats to reload. The reloading process could take between 30 seconds and 2 minutes.
The musket was a firearm and a front-loader, i.e. it was loaded with black powder and bullet from the front.
There were models with different firing mechanisms, the most common being the matchlock. This was very simple and moved a glowing match to the bassinet to release the shot. The bassinet is a small opening loaded with fine powder that ignites the powder inside the barrel.
In addition to the matchlock musket, there was also the wheellock musket. The wheel lock was more complicated (and therefore more expensive) and was not as reliable. The wheel lock had a wheel that had to be wound up so that when the trigger was pulled, a pyrite stone would hit the ignition powder and ignite it. The wheellock musket is more likely to be found among the nobility as a hunting weapon than on the battlefield.
The black powder was stored in small capsules (made of turned wood) attached to a belt. There were 8 - 14 capsules hanging from the so-called bandolier. Each capsule contained exactly the amount of black powder needed for one shot. The bullets were stored in a small leather bag, which was also attached to the bandolier. The fine powder for the bassinet was stored in a powderflask.
The musketeer/arquebusier could also have a harness, but usually only a breastplate, with or without a backplate and without tassels (thigh protection).
Their side weapon was a sword or rapier (with or without a left-handed dagger).
Cuirassier
The cuirassier belongs to the heavy cavalry and was in full armour. He was armed with 2 wheellock pistols, a lance and a sword. The lance dates back to the age of chivalry and was used less and less. Mainly Spanish cuirassiers still used the lance in the 30 Years War, but stopped, because it was more effective by making quick attacks with the firearm.
The sword was slightly wider and heavier and could be used as a cutting weapon from horseback.
Dragoon
The dragoon was a lighter cavalry unit and was actually more of a foot soldier who used a horse to be able to move more quickly (which does not mean that he never fought from horseback).
Therefore, his equipment hardly differs from that of the musketeer. He was armed with a musket or arquebuse.
His horse was also less well trained and therefore cheaper, because he might had to leave it back.