was a member of the Central Powers before the war, but switched sides when the Allies promised them some coastline on the Adriatic Sea that belonged to Austria-Hungary.

The Entente had many strengths: Britain had the strongest navy, and it was actually the naval blockade of the North Sea that partially caused the unrest that led to the abdication of the Kaiser in 1918. Britain was also the financial center of the world and could count on securing American loans. France and Britain could rely on calling up colonists to fight on their behalf. The Russian economy actually improved in the decade that followed the failed revolution in 1905. Though the nation still had trouble getting goods to troops at the front, conditions had improved since the Russo-Japanese War. The United States would be a reliable source of funding before its official entrance into the war in 1917.

The Entente had many weaknesses as well. The United States was slow to send troops to the front in 1917 because there were simply none available. Russia underwent a revolution due to political unrest, poor leadership by Czar Nicholas II, and the decline of Russian fortunes on the Eastern Front. British and French colonial troops were often treated poorly and were not as reliable as some hoped. No side was fully prepared to fight in the trenches and the Entente's generals' cavalier attitude about casualties almost led to mutinies on the front lines.

The Central Powers were well-positioned with internal supply lines—Germany and Austria-Hungary could theoretically help each other in the war. The German army was well-respected and well-supplied. While Germany had some overseas colonies, it was not as overextended as Britain and France.

The weaknesses for the Central Powers far outnumbered the strengths. Austria-Hungary had many ethnic divisions, and many troops from both the Czech Republic and Galicia refused to fight for an empire where they were marginalized. The Ottoman Empire had long been considered the "sick man of Europe" and ultimately fell due to groups pushing for independence on the Arab Peninsula. Germany was forced to fight a two-front war which turned into a war of attrition with the failure of the Schlieffen Plan. The German navy could not break through the minefields of the North Sea and Germany could not use its own propaganda arm to convince the United States that they were the "good guys" in this war. Germany was constantly forced to bail out Austria-Hungary in its war with Russia. German submarines were not enough to bring Britain to starvation though they were instrumental in bringing the U.S. into the war. Germany's backing of Lenin in 1917 ultimately backfired as the nation faced its own Bolshevik problems in 1918 and the period immediately thereafter.

The two opposing military alliances of World War I were the Entente Powers and the Central Powers. The Entente Powers were composed of France, Great Britain, the United States (after 1917), Italy (after 1915), Russia (until 1917) and Japan. The Central Powers were made up of Austria-Hungary, Germany, the Ottoman Empire, and Bulgaria. We will discuss their relative strengths and weaknesses below.

Entente Powers

Strengths

Taken together, these nations had large overseas empires to call on for material and personnel. Great Britain and France, in particular, had many colonies all over the world, particularly in Africa and southeast Asia. Laborers from these colonies, as well as some combat troops, greatly augmented the fighting forces of the Entente. Also, to support their previous imperial conquests, France and Great Britain had large and technologically advanced navies that would serve their alliance well during the war.

Russia did not have the large empire of its allies, but it did have a large domestic territory and a huge population. It was able to use its resources and large army to its advantage.

The United States and Japan were able to strengthen the alliance in a way that the other members could not. Since the war was not being fought on their soil, the manufacture of war materials and supplies was not disrupted.

Weaknesses

The Entente Powers were geographically spread out from each other. This meant that to supply their allies, each member nation had to risk a dangerous and lengthy ocean crossing. It also made communication more difficult.

Russia started off the war as a strong ally in terms of manpower and supplies, and Russia had the advantage of having a strategic eastern front. However, it soon proved to be as much of a liability as an asset. Internal unrest and a weak political structure led to a revolution that overthrew the tsar in 1917. The Central Powers were able to take advantage of this situation and by the end of the year, Russia was out of the war.

The Central Powers

Strengths

The Central Powers all shared borders with each other. Being contiguous, they were more easily able to supply each other with aid and personnel. This also made communication fast and simple.

Germany and Austria-Hungary had a strong military tradition long before the start of the war. They had large, well-equipped and well-trained armies that they were able to call upon as soon as hostilities began.

Weaknesses

Before the surrender of Russia, the Central Powers were fighting a two-front war. Having to divide resources between a western and eastern front was a major disadvantage.

While Germany did have a modern navy, taken as a whole, the naval powers of the Central Powers were no match in terms of size to those of the Entente.

In addition to fighting external enemies, Austria-Hungary was also beset by internal ethnic conflicts. It had to contend with several rebellions during the war that diverted a lot of its resources.

Even though they had banded together to form military alliances, there had been long-standing political tensions between all the members of the Central Powers. These historic tensions made the powers distrustful of each other and weakened their alliance's overall effectiveness.

The Central Powers, comprised of Germany, Austria-Hungary, and the Ottoman Empire, had fewer soldiers than the opposing force in World War I. During peacetime, their combined military forces totaled 1,242,000, while the Entente, made up of France, England, and Russia, had a peacetime force of 2,170,000. During the war, the German army totaled 2.15 million, and the Austrians totaled 1.3 million. The forces of the Central Powers were dwarfed by the forces of the Serbians, Russians, French, and Belgians, which totaled 5.6 million.

Despite the superiority of the Entente's forces, Germany and its allies were able to fight on two fronts and hold off an Entente victory for four years. Their military formations were superior to those of the Russians, as the Germans boasted better leadership by officers and better trained rank and file soldiers. However, the Entente had superior technical advantages, as the Germans struggled to use new technologies to their advantage and to transport their forces from the Eastern to the Western Front quickly once Russia dropped out of the war. Instead, Germany tended to rely on the bravery of its soldiers in battle. They required more technical expertise with weaponry—which they were to develop after World War I.

After the Battle of the Marne, the Germans settled into a stalemate. The Germans tried to end the stalemate, in which the opposing forces settled into trenches on the Western Front, with counterattacks and infiltration techniques that involved infantry companies accompanied by trench mortar companies and flamethrowers. The Entente forces did not initially understand these new tactics and kept trying to break out of trench warfare to resume a traditional battle approach with a mass of infantry.

While the German troops may have been better trained and tactically superior, they could not defeat the Entente forces, which had superior resources and manpower. Though the Americans struggled to arm and equip themselves once they arrived in Europe, they and the other Entente powers eventually wore the Germans down. By the end of the war, the Germans could not muster sufficient manpower to defeat the Entente.

Most of the tensions that provoked the First World War were caused by years of struggles for hegemony in the European continent by the Triple Alliance formed by Germany, Austria-Hungary and Italy (though Italy switched sides when it entered the war in 1915) and the Entente formed by Britain, France and Russia. Germany, in particular, seemed the most powerful of American enemies as it competed with Britain for world leadership. Americans feared that an expansion of German influence would lead to increased militarism and reduced democracy. Germany was a powerful military force and, as the war began, its army made important victories. However, as the war dragged on, neither of the two sides were able to force the other to surrender. Germany's naval dominance, an apparent strength, was the immediate cause for American entrance in the conflict. The German announcement of undistinguished submarine warfare led Americans to fear for the safety of their own merchant ships and thus come out of their neutrality. The ethnic tensions within Austria-Hungary and the Ottoman Empire were certainly one of the main weaknesses of American enemies.

There were two major strengths that the Axis Powers enjoyed in WWII.  (I am speaking mainly of Germany and Japan here.)  These were that A) they were much more ready to fight and B) they had more experience and better war plans than the Allies originally did.

When WWII broke out, the Germans and Japanese were ready to fight where the Allies were not.  The Axis had been planning the war and were naturally more prepared for it than the Allies.  The Germans had much better plans for the war (the new tactic of blitzkrieg) than the Allies had.  The Japanese were much more experienced at fighting because of their recent experience in China.

It is also worth mentioning that the Axis had better weapons in some significant ways.  For example, both the Germans and Japanese had better airplanes at first than the Allies did.