Offensive (military)
Theatre offensive: A theatre offensive can be a war and a dominant feature of a national security policy, or one of several components of war if a country is involved in several theatres such as the United Kingdom in 1941. In general theatre, offensives require over 250,000 troops to be committed to combat operations, including combined planning for different arms and services of the armed forces, such as air defence troops integrated into the overall plan for ground operations.

Strategic offensive: A strategic offensive is often a campaign and would involve the use of over 100,000 troops as part of a general strategy of the conflict in a given theatre. For example, the Operation Barbarossa was a theatre offensive composed of three distinct and inter-related campaigns in the Southern, Central and Northern parts of USSR territory. Soviet strategic offensive operations during World War II often involved multi-front coordinated operations. Along with the Wehrmacht operations on the Eastern Front of World War II, these were the largest military operations of the twentieth century. Strategic operations of the Red Army in World War II provides a listing of large-scale Soviet operations.
A strategic offensive is the aggressive expression of war planning and the use of strategic forces as a whole, combining all resources available for achieving defined and definitive goals that would fundamentally alter the balance of power between belligerents. However, the planning and execution of strategic offensives are always based on theoretical considerations because it is impractical, uneconomic and difficult to hide a full-scale rehearsal of large-scale operations.
A strategic offensive consists of simultaneous, tandem or phased operational offensives that seek to achieve specific operational objectives that eventually lead to the achievement of a strategic goal, usually a complete defeat of the opposition, but also destruction of a significant enemy force or occupation of strategically significant territory, such as the Manchurian Strategic Offensive Operation.
Any given strategic offensive is a derivative of a combination of factors such as national military doctrine, past military experience, and analysis of socio-political, economic and military circumstances.

See also: The best defense is a good offense
Military operation
Charge (warfare)

References: 

Sources: Glantz, David M., Soviet military operational art: in pursuit of deep battle, Frank Cass, London, 1991 ISBN 0-7146-4077-8
Glantz, David M., The Soviet strategic offensive in Manchuria, 1945: August storm, Frank Cass, London, 2003
Fulton, William B., Major General, VIETNAM STUDIES RIVERINE OPERATIONS 1966-1969, DEPARTMENT OF THE ARMY, U.S. Government Printing Office, WASHINGTON, D. C., 1985
Longmate, Norman. The Bombers. Hutchins & Co, 1983. ISBN 0-09-151580-7.
Isby, David C., Weapons and tactics of the Soviet Army, Jane's Publishing Company Limited, London, 1981

External links: Tactical Reasons to Advance