Strongholds are Squat settlement centres. They were generally founded during the original colonisation and those produced later are known as Newholds. Strongholds also often join together under Leagues to form defensive pacts.
Generally a Stronghold develops around a mine and its associated living quarter although some later developments were not associated with mining. A hereditary Lord ruled each stronghold and was protected and supported by the Hearthguard. The Hearthguard were the elite of a Squat army and the servants to the Lord while also protecting the Lord when he went to war. Each Stronghold had a group of Brotherhood or War-Brethren which formed the core of the Squat armed forces for the Stronghold. Every Squat had an obligated 30-70 year service period although they may not be called upon to fight until they had sired two sons and raised them to maturity. This helped protect the continuity of the race from the Stronghold's military activities. A Squat could then retire from active duty with his honour and probably some wealth and take up a position of responsibility in his family's business.
The Brotherhood was often also seen as a mercenary force. In times of peace warriors were traded for resources to either fight for the Imperium or for other strongholds. Another member of the aristocracy was the Warlord, a close relative of the Lord who was there to be placed in control of the Brotherhood in order to prevent Lords from wielding too much power and sending their troops into battles they should not be fighting. Other Lords would send their Brotherhoods on expeditions which range from locating other ancient and lost strongholds to a campaign against an alien race or piracy. Some Brotherhoods had totally turned to piracy and become known as Squat Reavers. When they returned to their stronghold they distributed the booty between the pirates and the Lord of the Stronghold.
Squats had a requirement to provide forces for the Imperial Guard and this often took the form of a detachment of the Brotherhood. Space Marines however have a low tolerance for mutants and so Squats weren't posted to places they were likely to meet the Adeptus Astartes.