The Triple Entente was an alliance formed in 1907 by France, Britain and Russia before the 1st world war. It was started by the French because they felt threatened by Germany and the triple alliance (Germany, Austria-Hungary and Italy)
Britain joined because they were worried about the German Navy. Finally Russia joined because they were worried about attacks from Germany and Austria-Hungary who both had growing armies. Russia also promised Serbia help if they were attacked.
The Triple alliance
The Triple Alliance was formed in 1879. At first it just included Germany and Austria-Hungary because they would support each other if they were attacked by either Russia or France. Later in 1882 Italy was included to form The Triple Alliance.
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As you can see the Triple Entente have the advantage of a large navy and should be able to control the waters, they can win sea battles and transport troops across the sea.
The Triple Entente also have a larger overall population therefore more people will be able to make weapons, ammo ect. And support their country. Britain especially has a lot of support from colonies which should help a lot. Because of the large population the Triple Entente have a lot more money to spend on armed forces than The Triple Alliance so they should be able to train more men, have more ammo, better guns and artillery.
Unfortunately The Triple Alliance have more men than us which could give them an advantage. However most of them are very undisciplined and have very little training unlike Britain who's troops are extremely well trained. Because of this having less men might not be such a problem.
If the war takes place it's likely to be fought in Trenches. This could be a problem for us as currently the British army is only equipped with small shovels which aren't of much use for digging deep trenches. It's recommended that Britain should supply full size spades to the army like in France and