The French Army comprised approximately 400,000 regular soldiers, some of them veterans of previous French campaigns in the Crimean War, Algeria, the Franco–Austrian War in Italy, and in the Franco–Mexican War.
Generally the quality of the Imperial French army was high, while that of the Republican army was low but very variable.
The Imperial Guard should be rated as elite. The Chasseurs, the 'African' troops (Turcos and Zouave) and the cavalry should be rated as crack. While the rest of the field army are veteran.
For the 'Republican' period the remnants of the Imperial army should follow the guidelines above, with units such as the marines, sailors and the foreign legion counting as crack. The new units raised by the republic were generally bad and should be mostly uneducated levy (Mobile guard and irregulars).
The Prussian Army was composed not of regulars but conscripts. Service was compulsory for all of the men of military age, and thus Prussia and its North and South German allies could mobilise and field some 1.2 million soldiers in time of war.
The bulk of the German forces should be rated as Veteran with the following exceptions. Guard units should be rated as Crack or Elite, while Jagers should be Crack. Bavarian, Wurttemberg and Baden (the south German) line units was not very committed. Landwehr units should similarly be considered, even if they are much more educated reserve than their French counterparts.
Finally German cavalry was not of the highest standard and should be average or below. The exception to this was the Saxon cavalry, which was above average and should be rated as Crack.

One the French side, the infantry were equipped with the breech-loading Chassepot rifle, one of the most modern firearms in the world at the time, it had a maximum effective range of some 1,500 metres (4,900 ft) with a short reloading time. On the Prussian side, the army was still equipped with the "needle-gun" Dreyse rifle, which was by this time showing the age of its 25 year old design.
The French artillery was equipped with rifled, muzzle-loaded "4-pounder" guns. In addition, the army was equipped with a precursor to the machine-gun: the mitrailleuse, which could unleash significant, dangerous, concentrated firepower, with a weakness of having short range and relative immobility and thus prone to being easily overrun. It was developed in such secrecy, however, that no real training with the weapon was effected, and French gunners had no practical experience using it in combat. It was therefore treated like a piece of artillery, and in this role it was ineffective.
On the Prussian side, the deficiencies of the needle-gun were more than compensated for by the famous Krupp 6-pounder (3 kg) steel breech-loading cannons being issued to Prussian artillery batteries. The Krupp gun had a range of 4,500 metres (14,800 ft) and blistering rate of fire compared to the French bronze muzzle loading cannon.

French tactics emphasised the defensive use of the Chassepot rifle in trench-warfare style fighting ; German tactics emphasised encirclement battles and using artillery offensively whenever possible.

The French army was nominally led by Napoleon III with Marshals Francois Achille Bazaine, Patrice de Mac-Mahon, and Jules Trochu among others.
The Prussian army was commanded by Field-Marshal Helmuth von Moltke and the Prussian General Staff. The Prussian army was unique in Europe for having the only General Staff in existence, whose sole purpose was to direct operational movement, organise logistics and communications, and develop the overall war strategy.

"Imperial" part of the war
The efficiency of German mobilization contrasted with confusion and delay on the French side. Germany was able to deliver 380,000 troops to the forward zone within 18 days of the start of mobilization on 14 July, while many French units reached the front either late or with inadequate supplies. The German and French armies that then confronted each other were both grouped into right and left wings. After suffering a check by the Crown Prince and General von Blumenthal at the Battle of Wörth on 6 August 1870, the commander of the French right (south) wing, Marshal Patrice MacMahon, retreated westward. That same day, about 40 miles (64 km) to the northwest, the commander of the French left wing, Marshal Achille Bazaine, was dislodged from near Saarbrücken and fell back westward to the fortress of Metz. His further retreat was checked by the German right wing in two blundering battles on 16 and 18 August, respectively (the Battles of Mars-la-Tour and Gravelotte), and he then took refuge behind the defenses of Metz until forced by starvation to surrender on 29 October.
The French right wing, commanded by MacMahon and accompanied by Napoleon III himself, attempted to relieve Bazaine but was itself surrounded and trapped by the Germans in the disastrous Battle of Sedan on 31 August. Encircled, the 83,000 French troops with Napoleon III and MacMahon surrendered on 2 September. Since Bazaine's army was still bottled up in Metz, the result of the war was virtually decided by this surrender.

"Republican" part of the war
Yet this did not end the war, as the Third Republic was declared in Paris on 4 September 1870 and French resistance continued under the Government of National Defence and Adolphe Thiers. Over a five-month campaign, the German forces defeated the newly recruited French armies in a series of battles fought across northern France. Following a prolonged siege, noted for the first use of anti-air artillery, Paris fell on 28 January 1871. Ten days before the fall of the city, the German states proclaimed their union as the German Empire under the Prussian king, Wilhelm I, uniting Germany as a nation-state. During the time of the Paris Commune uprising, the final Treaty of Frankfurt was signed 10 May 1871. The settlement gave Prussia the French territories of Alsace and part of Lorraine to become part of the new Germany.

General Staff system
The Prussian General Staff developed by Moltke proved to be extremely effective, in contrast to the traditional French school. The structure also greatly strengthened Moltke's ability to control large formations spread out over significant distances. The French General Staff—along with those of every other European military—was little better than a collection of assistants for the line commanders. This disorganization hampered the French commanders' ability to exercise control of their forces.

Universal conscription
Two major reforms substantially increased the military power of Germany. The first was a reorganization of the army that integrated the regular army and the Landwehr reserves. The second was the provision for the conscription of every male Prussian of military age in the event of mobilization. Thus, despite the population of France being greater than the population of all of the German states that participated in the war, the Germans mobilized more soldiers for battle.

Mobilization system
At the outset of the Franco–Prussian War, 462,000 German soldiers concentrated flawlessly on the French frontier while only 270,000 French soldiers could be moved to face them, the French army having lost 100,000 stragglers before a shot was fired through poor planning and administration.

Armaments
The French breech-loading rifle, the Chassepot, had a far longer range than the German Dreyse needle gun; 1,600 yards (1,500 m) compared to 600 yd (550 m). They also possessed an early machine-gun type weapon, the mitrailleuse, which could fire its twenty-five barrels at a range of around 2,000 yd (1,800 m). The French were equipped with bronze, rifled muzzle-loading artillery, while the Prussians used new steel breech-loading guns. The breech-loaders had a far longer range that the muzzle-loading guns, and could be fired faster.

Line, light (Jaeger), Reserve (Landwehr) :

Guard, Light (Guard Schutzen), Reserve (Guard Landwehr) :

Cuirassier, Uhlan, Hussar, Dragoon :

Guard and line artillerists, Krupp breachloading canon and caisson :



Harnessed caissons, officer :

Line and light soldiers :