From a gentry family, he served as a page at the court of the House of Stuart under James, Duke of York, through the 1670s and early 1680s, earning military and political advancement through his courage and diplomatic skill.

William recognised his abilities by appointing him as his deputy in Southern Netherlands (modern-day Belgium) before the outbreak of the War of the Spanish Succession in 1701, but not until the accession of Queen Anne in 1702 did he secure his fame and fortune.

As de facto leader of Allied forces in the Low Countries, his victories at battles of Blenheim (1704), of Ramillies (1706), of Oudenarde (1708), and of Malplaquet (1709) ensured his place in history as one of Europe's great generals.

[22] Churchill was reportedly concerned at being too closely associated with James, particularly since Sarah's sister Frances was married to Irish Catholic Richard Talbot, appointed Lord Deputy of Ireland in 1687.

This provides the immediate context for Delamere's acquittal but shortly after the Coronation, Churchill reputedly told French Protestant Henri de Massue that "If the King should attempt to change our religion, I will instantly quit his service.

[28] James II's promotion of Catholics in royal institutions – including the army – engendered first suspicion, and ultimately sedition in his mainly Protestant subjects; even members of his own family expressed alarm at the King's zeal for Roman Catholicism.

The signatories to the letter included Whigs, Tories, and the Bishop of London, Henry Compton, who assured the Prince that, "Nineteen parts of twenty of the people ... are desirous of change".

[39] His task was urgent, for less than six months after James II's departure, England joined the war against France as part of a powerful coalition aimed at curtailing the ambitions of Louis XIV.

However, at the Battle of Walcourt on 25 August 1689 Marlborough won praise from the Allied commander, Prince Waldeck – "despite his youth he displayed greater military capacity than do most generals after a long series of wars ...

Although the campaign did not end the war in Ireland as Marlborough hoped, it taught him the significance of the minutiae of logistics, and the importance of cooperation and tact when working alongside other senior Allied commanders.

Macaulay states that in a letter on 3 May 1694 Marlborough betrayed the Allied plans to James, thus ensuring that the landing failed and that Tollemache, a talented rival, was killed or discredited as a direct result.

Lady Marlborough was made Groom of the Stool, Mistress of the Robes and Keeper of the Privy Purse giving them a combined annual income of over £60,000 and unrivaled influence at court.

[h] However, Marlborough's hopes of founding a great dynasty of his own reposed in his eldest and only surviving son, John, who, since his father's elevation, had borne the courtesy title of Marquess of Blandford.

[73] Concerns over Vienna and the situation in southern Germany convinced Marlborough of the necessity of sending aid to the Danube, but the scheme of seizing the initiative from the enemy was extremely bold.

However, the main event followed on 13 August when Marlborough – assisted by the Imperial commander, the able Prince Eugene of Savoy – delivered a crushing defeat on Marshal Tallard's and the Elector of Bavaria's army at the Battle of Blenheim.

The whole campaign, which historian John A. Lynn describes as one of the greatest examples of marching and fighting before Napoleon, had been a model of planning, logistics, tactical and operational skill, the successful outcome of which had altered the course of the conflict – Bavaria was knocked out of the war, and Louis XIV's hopes of an early victory were destroyed.

[77] The Queen lavished upon her favourite the royal manor of Woodstock and the promise of a fine palace commemorative of his great victory at Blenheim; but since her accession her relationship with Sarah had become progressively distant.

For her part, Anne, now Queen and no longer the timid adolescent so easily dominated by her more beautiful friend, had grown tired of Sarah's tactless political hectoring and increasingly haughty manner which, in the coming years, were to destroy their friendship and undermine the position of her husband.

Although Marlborough penetrated the Lines of Brabant at Elixheim in July, indecision and Dutch objections (concerned as they were for the security of their homeland), prevented the Duke from attacking the French at the Dyle.

As a price for supporting the government in the next parliamentary session, the Whigs demanded a share of public office with the appointment of a leading member of their Junto, the Earl of Sunderland (Marlborough's son-in-law), to the post of Secretary of State.

[86] The Queen, who loathed Sunderland and the Junto, and who refused to be dominated by any single party, bitterly opposed the move; but Godolphin, increasingly dependent on Whig support, had little room for manoeuvre.

[96] His subsequent victory at the Battle of Oudenaarde on 11 July 1708 demoralised the French army in Flanders; his eye for ground, his sense of timing and his keen knowledge of the enemy were again amply demonstrated.

[101] However, Allied demands at the peace talks in The Hague in April 1709 (principally concerning Article 37 that bound Louis XIV to hand over Spain within two months or face the renewal of the war), were rejected by the French in June.

Yet the cost was high: the allied casualty figures were approximately double that of the enemy (sources vary), leading Marlborough to admit – "The French have defended themselves better in this action than in any battle I've seen".

The Cabinet had long lacked cohesion and mutual trust (particularly following the Sacheverell affair) when in the summer the plan to break it up, prepared by Harley, was brought into action by the Queen.

[112] By an exercise of brilliant psychological deception,[113] and a secretive night march covering nearly 40 miles in 18 hours, the Allies penetrated the allegedly impregnable lines without losing a single man; Marlborough was now in position to besiege the fortress of Bouchain.

But these assurances against a Jacobite restoration (which he had been taking out since the early years of William III, no matter how insincere), stirred Hanoverian suspicions, and perhaps prevented him from holding the first place in the counsels of the future George I.

Robert Parker, who served under Marlborough, writes: in the ten campaigns he made against [the French]; during all which time it cannot be said that he ever slipped an opportunity of fighting when there was any probability of coming at his enemy: and upon all occasions he concerted matters with so much judgment and forecast, that he never fought a battle which he did not gain, nor laid siege to a town which he did not take.

His determination to preserve the independence of the Queen's administration from the control of the party faction initially enjoyed full support, but once royal favour turned elsewhere, the Duke, like his key ally Godolphin, found himself isolated; first becoming little more than a servant of the Whigs, then a victim of the Tories.

Aided by an expert staff (particularly his carefully selected aides-de-camp such as Cadogan), as well as enjoying a close personal relationship with Eugene of Savoy, Marlborough proved far-sighted, often far ahead of his contemporaries in his conceptions, and was a master at assessing his enemy's characteristics in battle.