If you want to have Britain fighting alongside Germany in WWI, you have to nip the Entente Cordiale in the bud. The best way to do this is escalating the Fashoda Incident.
1898
The French do not relinquish their claims in southern Sudan and instead of retreating they reinforce Fort Saint Louis at Fashoda to complete their belt of colonies from Dakar to Djibouti. The Anglo-Egyptian Commander sends gun-boats and after an ultimatum to abandon Fort Saint Louis is not met by the french forces under the command of major Jean-Baptiste Marchand he orders the shelling of said fort. Major Marchand and a couple of his tirailleurs d'Afrique are killed and the french dreams of a belt of colonies from the west to the east coast of Africa are destoyed. The french press blows the small shoot-out completely out of proportion and there are attacks on british travellers in France.
1899
The second Boer War starts. With the goal to destabilize the grip of the British over their African colonies France starts to covertly aid the Boers by selling them weapons and military instructors.
1900
The covert french aid for the Boers becomes public and instead of denying the undeniable the french government goes for broke and does not only recognize the Boer republics diplomatically, but declares them to be under french protection. Out of protest over this act Britain first retreats from the 1900 World Fair in Paris and then even recalls its ambassador. Open war between France and Britain seems increasingly likely.
1901 - 1902
A German and American attempt to mediate the ongoing crisis is finally successful. The French are forced to withdraw their military instructors and the Boer republics become parts of the British Empire. The Americans were in favour of an independence for the 2 republics, but Germany sided with Britain and the result was a dominion status of the Orange Free State, Transvaal and Natal within the British Empire.
1902
The Anglo-Japanese Alliance is signed.
1904 - 1905
The Russo-Japanese War ends with the Japanese victory and the Peace Treaty of Portsmouth.
1907
France and Russia sign the Entente Cordiale. The great game between Britain and Russia continues over the control of Qing China.
1911
After a rebellion in Morocco french forces occupy the cities of Fez and Rabat, officially to protect life and property of french and other european citizens, but plans become public that France intends to force Morocco to become a french protectorate. Britain and Germany, not willing to accept a french encroachment of Morocco send gunboats of their own. The United States mediate and Morocco becomes a united Anglo-German protectorate.
1912
The french general staff is aware that Germany significantly outproduces France. A plan is prepared to strike at the heart of german industrial production in the Ruhr region. The plan is to coerce Belgium and if necessary the Netherlands into letting the french forces march through and to occupy the territory between Aachen, Cologne and Duisburg, then to cross the Rhine and conquer and hold as much of the Ruhr Region as possible, at least up to Hagen and Dortmund, if possible up to Unna and Hamm. If the territory connot be held later, the industrial capacity is to be destoyed.
1914
Archduke Franz Ferdinand is severely wounded, his spouse Sophie Chotek killed when a bomb, thrown into their car detonates during a visit to Sarajevo. When it's found out, that the Serbian Secret Service aided in this assasination plot and Serbia, backed by Russia proves intransigent to Austro-Hungarian demands, Austria Hungary declares war on Serbia, Russia thereafter declares war on Austria Hungary, Germany declares war on Russia and France declares war on Germany. When Belgium proves intransigent to french demands to let french forces march through, France occupies the south-eastern part of Belgium and attacks Germany. Britain issues an ultimatum to France to withdraw its forces from Belgium within 48 hours or a state of war will exist between the United Kingdom and the French Republic ...