Why Does The Country Declare War?

From Napoleonic wars of the 19th century to the early 20th century,nearly half of interstate wars were accompanied by declarations of war.European countries showed a general trend of declaring war when they launched a war against each other.Why did the European countries be more likely to declare war from 1815 to 1914 than after World War I ?This paper holds that there is correlation between the two elements of the multi-polar balance system in Europe-the principle of intervention of great powers and the instability of alliance and the declaration of war on European countries.Through the comparative analysis of the war between European countries after 1820,the question can be explained by the fact that if the state does not carry out the declaration of war against other countries,it will give the reason for the intervention of the other great powers.The great powers,through diplomatic intervention,sanctions or direct military interference,will reduce the probability of the country to win the war,and the country's expected war dividends will be greatly reduced.On the other hand,under the multi-polar balance of power system,the state can be based on short-term interests of the alliance,There are many powerful "coalition barriers" that are suitable for all potential partners.In this case,in order to increase the weight of the war victory,a nation will sign a neutral or military alliance treaty with other countries according to different situation.If the state does not declare war,the neutral and alliance treaties will not be able to start,and the victory of the war will become more difficult.Therefore,belligerents will be generally chosen to declare war.