In the Marxist view, it is not only true that in a capitalist age wars are a necessary and unavoidable outcome of the mode of production and only the proletarian revolution can stop them breaking out or violently interrupt the course of them.
It is also true that in certain periods, i.e. periods of crisis in the mechanisms of accumulating capital, war is the extreme remedy that the bourgeoisie cannot help turning to, to protect their own dominion through the mass destruction of capital, goods and the labour force: briefly, people and what they produce with their own hands.
This does not mean that the bourgeoisie enters a war according to carefully pondered calculations or free decisions made by their legislative or executive bodies:  it is the very existence of capitalism, its vital needs, that set off the mechanism of the conflict – starting from the preliminaries to what will then become the formal declaration of war, right up to its practical, material and ideological practice.
War does not break out either “by chance” or “by design” on the part of individuals or groups:  it is the ultimate outlet for an objective situation that has developed in a whole range of sectors and has exploded at a breaking point in the balance of power between the economies of countries that are candidates for the role of belligerents.
The prime objective of capital, once invested, is to reproduce itself with a profit. It is therefore accumulation that dominates the entire cycle of capitalism’s operation, making it necessary to extend production and the corresponding areas of outlet beyond all limits. It is competition, at each phase of the accumulation process, that selects and causes clashes, first in private capital (or, briefly, individual capitalists) and then – as the demands of accumulation become more pressing –  joint stock companies, trusts, multinationals: to sum up, businesses that tend to be or actually are monopolies, whose interests generally do go beyond national borders but which find their political expression and the guarantee for their interests in the national state, the great and powerful machine organized to defend them.
Whilst – from a technical point of view – the production process grows without pauses or limits, gaining its impulse from the volcanic nature of the production of goods itself, there is a tendency for there to be fewer possibilities for placing products in the “profitable” conditions  that are essential if the process of accumulation in these given conditions is not to be interrupted: the “volcano of production” tends to find its counterpart in the “swamp of the market”, which, instead of widening, remains stagnant. This is when the most violent of its contradictions explodes at the heart of the capitalist economy – here the crisis of  the system makes it necessary to turn to extreme solutions in terms of the use of force.
In industrially more advanced countries, the countries of the “old” capitalism, the entrepreneur class encounters serious limits to the investment of accumulated capital, or the lack (or partial lack) of local raw materials or a native labour force, or markets where the goods produced can be sold.
And stocking up on raw materials not available locally, the hiring of foreign labour, the conquest of foreign markets today are processes which, far from being successfully achieved purely by economic means or by the game of competition, imply a constant effort to regulate and control purchasing and selling prices and the privileges that are gradually obtained through state measures or agreements between states.
Thus economic expansion tends to become transformed from competition into monopoly and find its typical expression, supported where necessary by powerful military forces, in the form of finance. It is a matter of controlling large mining resources, or human masses to be made into proletarians, or outlet markets that can absorb the products of capitalist industrialisation, the power to decide the outcome of a race to corner a sector, to control or directly dominate increasingly large sectors of the world economy.  The global manifestation of the clashes and crises that result from this is imperialism, which from an economic point of view takes shape in the process of concentration, where the point of arrival is the monopoly organisation of production and exchange.
Through financial capital, the powers of America, Japan, Germany and other European and non-European (China) countries manoeuvre the world economic scene without opposition, ready to throw themselves into one adventure or another (there is certainly no lack of examples, even limiting ourselves to the last fifteen years or so), in order to conclude one form of alliance or the other or, vice-versa, to threaten and finally attack each other, just as long as they react against the downward trend (and in times of crisis actual fall) in the average profit ratio.
But this is a position that is only reached by securing and attempting to maintain a position of power over competitors both nationally and internationally and, when two or more imperialisms with irreconcilable vital interests clash, this necessarily sets off that typical mechanism of capitalism, which is inevitable in it, in the form of armed conflict. The objective of it is not only to overcome, at least temporarily, a crisis at the adversary’s expense, thanks to gaining more advantageous positions in the exploitation of resources and labour in the country or countries defeated, but also (and above all) to re-launch the cycle of accumulation of capital through the large-scale destruction of goods and the labour-force and through the subsequent orgy of re-building – a common objective (this is the key point) of friends and enemies, belligerent and non-belligerent, winners and losers.

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Marxist revolutionaries are well aware of all these issues by now and their solution distinguishes them quite clearly from all the political and social forces that believe it possible and, what is more, effective, for humanity to fight against the regime and logic of monopoly, for an equal division of resources between states and their pacific co-existence in an atmosphere of justice, if not of brotherhood.
For Marxism, no therapy or clinical treatment is of use within the capitalist mode of production for limiting and finally getting rid of the plague of inter-imperial clashes.  We cannot be pacifists or “against war”:  this would mean admitting the possibility of eliminating war before eliminating the capitalism that fuels it and makes it necessary – for this very reason, it would mean harnessing the proletarian masses even more closely to capital (and therefore to war itself), distracting them from their historical class commitment. All the peace-keeping propaganda against “provokers” who are supposed to be those responsible for the armed conflicts (“aggressors”, “terrorists”, “renegade states”, “empires of evil”, etc. in the squalid rhetoric of  contemporary bourgeois ideology) is not only devoid of any serious content for us, but actually works against the ultimate aims of the struggle for the emancipation of the proletariat and, with it, of the whole of humanity.
For proletarians, it is not a problem of taking ranks on one side or the other, in defence of postulates that range, according to the occasion, from individual liberty to political democracy, from equality amongst human beings to “socialism in a single country” and its defence, from human rights and those of the citizen to safeguarding “people’s rights”, and which all converge in an effort to keep alive a mode of production and a society that drips blood from every pore.
The vicious circle of crises and wars, which forms the very substance of capitalism’s process of development, must be broken: and only the communist revolution can break it.
Recognizing this is also the condition for the defence of the immediate living and working conditions of the proletariat, since it is through cooperation between classes inseparably linked to pacifism and the national solidarity propounded by bourgeois defensive tactics that the unity of the class in its fight against capital is compromised.