Strategy:
Origin: in the early 19th century: from French stratégie, from Greek stratēgia 'generalship', from stratēgos .
[mass noun] archaic (ancient) skill in devising plans or schemes; “cunning”.
Strategy involves a high level of careful plans or methods to achieve one or more goals under conditions of uncertainty.
Strategy is also about attaining and maintaining a position of advantage over adversaries through the successive exploitation of known or emergent possibilities rather than committing to any specific fixed plan designed at the outset.
The science and art of using all the forces of a nation or group of nations (an alliance) to execute approved plans as effectively as possible during peace or war.
In contrast to the term ‘Tactics’, it is a particular long-term plan for success, especially in business or politics.
The skill of developing and employing instruments of national (or international) power in a coordinated and integrated fashion to achieve national (or multinational) objectives.
In military theory, strategy is "the utilization during both peace and war, of all of the nation's forces (political, economic, psychological, and military), through large scale, long-range planning and development, to ensure security and victory".
Stratagem:
A devious trick for deceiving or surprising an enemy.
A plan or scheme, especially one used to outwit an opponent or achieve an end.
Any artifice or ruse devised to attain a goal or gain an advantage.
A clever, often underhanded scheme for achieving an objective.
In some details:
Strategy (Greek "στρατηγία" - stratēgia, "art of troop leader; office of general, command, generalship") is a general, undetailed plan of action, encompassing a long period of time, to achieve a complicated goal.
Strategy, as a way of action, becomes necessary in a situation when, for the direct achievement of the main goal, the available resources are not enough. The task of