Side note: I've skipped the half-elves because they do not have a separate community of their own so they technically are not a race per se.
Tight-knit halfling communities are found near the settlements of other races, often along or even on the surface of a body of water. Halflings have never built a kingdom of their own or even held much land. They don’t recognize any sort of royalty or nobility of their own, instead looking to family elders to guide them. This emphasis on family and community has enabled halflings to maintain their traditional ways for thousands of years, unaffected by the rise and fall of empires. (Player's Handbook, pg. 45)
Halfling communities are sort of an enigma. It has been taken granted that they will always be there but no one pays them any attention. Halfling communities have always lived in the shadow of their taller neighbors. Although they have been known to co-exist very well with other races but it is their promiscuity that has always keep them away from trouble.
Their friendly and peaceful nature makes them one of the least warlike races and no other race ever sees them as a threat. Halflings are willing to maintain good trading relations with whoever that happens to be their neighbor at a particular point in time and do not stick their nose into political matters that are not their own. They are always neutral in any conflict and their friendliness makes it hard for them to make enemies.
Halfling settlements have been known to be a good source of food, drink and other basic necessities and conquerors have always considered that it is best to leave them alone for that reason.
Halflings in Times of War
Most halfling communities have seen and been through many wars but to them it is mainly a subject of curiosity and novelty. War also does not destroy trading opportunities but rather it creates them. A halfling spice merchant who frequently travels to a human town to trade may return and tell his fellow merchants that a group of burly orcs have moved into the neighborhood and they need a good beef supply.
Halflings are an optimistic folk. Their cheerfulness is maintained even before, during and after wars. Wars that happen outside their community are regarded as though it never involves them, which is usually the case. It has been a way of live for halflings to never bother or be bothered by such affairs. They live in a world of their own.
A traveler who enters into a halfling village will find that the atmosphere of war and anxiety are absent. The music are still lively in their taverns, the woman and children are out in their fields and the halfling merchant is only concerned about when he needs to restock his goods. Halflings genuinely just want to have fun and enjoy their communal lifestyle which they don't need to be reminded about.
However, a halfling knows when there is a time to defend themselves and they pride themselves of keeping their borders safe for anyone who ventures into them.
Most wandering halfling clans have a number of bounders who serve as scouts. These warriors help keep the traveling band carefree—they put down dangers before the threat becomes dire. (Martial Power, pg. 28)
Although civilized armies don't normally pose a threat to a halfling community but it is the savage monsters of the wilderness that halflings have to face to keep their homes secure. Occasionally, a deadly beast would wander into the fertile lands near the rivers where halflings build their settlements and waylay travelers and merchants alike. Sometimes halfling scouts would spot these emerging threat before they can do any serious harm to their village and a quick effort is made to sedate that threat immediately.
The world is wide and wild, and the nomadic halflings are small folk. Deftness and quick wits have
allowed them to survive nonetheless. As they have done so, they have come to rely on wily and daring warriors to protect them. Even settled halflings maintain a soldierly class to see to their interests among other, and larger, civilized folk. (Martial Power, pg. 28)
Halfling armies are only as large as their stature which are only sufficient for self defense and minor skirmishes with singular or small number of monsters. It does not even have a complicated structure. A regular soldier are called stouts and the highest rank that one can attain in a halfling army is captain who is the commander of the army.
Stouts are divided into platoons each headed by a platoon leader who relays the direct orders from the captain to the platoon members. Normally the leaders are the most resourceful members in the platoon but they do not outrank any of their comrades, merely the lucky ones who get selected.
Halfling in the Battlefield
Quick and resourceful wanderers, small in stature but great in courage (Player's Handbook, pg. 44)
Halfling armies are very mobile and they move quickly around the battlefield. They don't fight toe-to-toe with their enemies in a rank and file formation unlike most armies do. They strike their enemies at all sorts of angles and then just as they appear to be withdrawing, they run right back into the fray.
Halflings are also resourceful which means that they improvise in battle. Halflings are well known to be brilliant tacticians in using the terrain of the battlefield to turn against their enemies. If given the time and place to prepare, halflings tend to design elaborate traps that will hinder the maneuverability of their enemy such as pit traps or net traps. They would also lure their enemies into tight spaces where their small size becomes an advantage.
But in the end when it comes down to a fight, halflings are no cowards. Fighting with halflings can be a very confusing and messy. They don't charge straight at the enemy, they charge into the enemy. Using their size as an advantage, halflings tend to run in between enemies before they strike. They willingly expose themselves as fast moving targets which opponents can find it very difficult to keep up. Sometimes this creates such a confusion that enemies hit their own comrades in their frustrating effort to get the dodging halfling.
Halfling soldiers are trained in two different fighting styles that are unique to halflings. One is called bounding, the other is dancing.
The fighting tradition of the halfling bounder favors halfling traits. Bounders are practiced in hit-and-run strategies and pack tactics. They spring about the battlefield, avoiding the attacks of their
bigger enemies, striking from unexpected angles, and making harrying assaults. Bounders willingly lay down their lives to allow those they care for to survive and escape danger. (Martial Power, pg. 28)
Bounders, as they are called, are combat acrobats. They perform jumps, flips, sommersaults and tumbles to stike multiple targets on the run. They are always on the move to prevent themselves from being an easy target, causing confusion and distractions at the same time.
Halflings have long used music and a sense of fun to enliven physical labor and various dull tasks. When the race was young, they created dancelike movements that mimicked martial skills—and translated into deadliness in melee. Halflings learned that bladed weapons lent themselves easily to such a refined use. As their battle dances evolved, halflings began to consider the nimble use of a pair of bladed weapons a refinement of the style. (Martial Power, pg. 60)
Dancers are deadly single combatants that perform their blade dances across the battlefield. Their turns, swirls and footwork allows them to dodge and riposte many attacks which makes unpredicatble and deadly. A halfling army with dancers are accompanied by a musician trope that plays the music in the distance to set the rhythm of the dance.
Then there are those who do not rely on fancy footwork and flashy acrobatics. Prowlers would sneak up to an enemy amidst the commotion and hamstring him before slitting his throat.
Tactics & Strategy
Halflings prefer to use stealth first rather than array themselves before their enemies. Halflings would first use sniping tactics with their slings from cover as long as they can. Once their cover is blown then do the bounders and dancers charge out to face the enemy.
Once in melee combat, halflings don't usually fight alone. They use their size and speed to set up flanks and outnumbering a single opponent to make them easier to take down. Also because of the chaotic situation which halflings create and given the height difference in hand to hand combat, slingers would still continue to bombard the enemies with shots, aiming for the taller parts of their bodies without hitting their own comrades.
Halflings have a long tradition of using light blades with great skill. Whether a tool of survival or an
implement of battle, the simple dagger has much to recommend it. Even one as small as a halfling can hide a dagger on the body for use in a tight spot. A small body coupled with a small weapon means greater mobility and deadliness enhanced by a better chance for stealthy attacks.
Halflings also have a history of using light blades in their art and performances. Carving, acrobatic
blade tricks, knife juggling, dagger throwing, and even dances that incorporate blades are common among halflings. For them, such activities are a natural meeting of physical traits and handy tools. (Martial Power, pg. 94)
The weaponry of a halfling soldier is simple. He carries a sling with a pack of stones on one hand and a short sword or dagger in the other. Halflings know very little about the ways of forging heavy and large steel swords but it doesn't suit them due to their size and agility anyway. The light blade is more of an essential tool that also acts as a weapon.
They also wear light armor such as leather for minimal protection that will not hamper their movement and speed. They have no use for metal armor and they don't have armorsmiths that can create a proper suit.
Halflings do not have any magical equipment that can aid them so they rely heavily on the craftsmanship of those who made their weapons and armor.