In 2009, I thought to make a TL about a surviving Second French Empire. I thought first to take a french victory in Franco-Prussian War as POD. After realizing it would be hard and a little implausible, I decided to prevent the Mexican Expedition with a POD in late 1857.
For the previous two years, I've been collecting informations, ideas to make the TL. The version I present you today is destined to prepare a v2.O more realistic. In fact, I am just beginning to make serious searches with the reading of books instead of searches on the web. I'm aware that I will make several mistakes; please correct me.
The title 'War and Peace' is provisory; I will take an other title for v2.0.
Chapter One
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Reform War
Plan de Tacubaya
Since 1855 and the fall of Santa Anna's regime, the federalist and anti-clerical Liberals and the centralist and clerical Conservatives struggled again for control of the country.
In 1857, the former issued a new constitution establishing a federal state, what angered the Conservatives and caused a coup.
On 17th december 1857, General Felix Maria Zuloaga proclaimed the Plan de Tacubaya, declaring abolished the new constitution. Soon , President Comonfort announced his support for the coup. Only some in the Congress attempted to oppose the coup but were quickly arrested. All seemed to go well, but on December 21th, the state of Jaliso declared his opposition to the Plan de Tacubaya. The abolition of a constitution which granted them great autonomy prompted the other states to follow Jalisco, and by early January 1858, only the capital and Veracruz were firmly under Conservative control [1].
What's more, the conservative junta soon turned against President Comonfort, proclaiming General Zuloaga as President. On January 21th, Comonfort finally went into exile after a week of clashes between soldiers of the junta and his partisans. Benito Juarez, that he had freed before leaving, had set up at Guanajato a new government as soon recognized by the Constitutionalist states.
President General Felix Zuloaga
'The valiants don't murder' _ 1858
Civil war began badly for Juarez. On March 8th and 9th, the 5.000 men of Conservative general Osollo defeated 7.000 Constitutionalists under General Parrodi at Celaya then at Salamanca. Guanajato surrendered on March 12th.
'The valiants don't murder' said Guillermo Prieto the day after, saving lives of Juarez and his ministers. Indeed, a colonel Landa had taken control of Guadalajara where the government had fled, but convinced by the poet, the soldiers entrusted with the execution renounced, and in a day, the mutiny was over [2].
However, Guadalajara was taken 11 days later. Juarez, who had just lost his two first capitals, settled at Monterrey a month later [3].
President Benito Juarez
On April 10th, the Constitutionalists suffered three defeats: General Echeagaray's army, aimed at taking Monterrey, took Tampico, while Morelia fell to General Gomez, and that General Miramon entered without resistance in Zacatecas.
But by late April, they began to score victories: General Zuazua retook Zacatecas on April 27th then San Luis Potosi on June 30th. On May 29th, Echeagaray's advance on Monterrey was halted at Montemorelos.
General Santos Degollado, commander of northern and western armies since April 7th, even threatened Guadalajara, although he was repulsed at the battle of Atenquique on July 2nd [4].
The Constitutionalist resurgence was halted by the victories of General Miramon at the battle of Ahualulco de Pinos on September 27th, which allowed to take once again San Luis Potosi, and Zacatecas a month later, and in the Santiago river campaign which culminated with the battle of the San Miguel ranch, on December 15th, what forced General Santos Degollado to abandon the siege of Guadalajara.
Plan de Navidad
On December 23th, a group of officers led by General Echeagaray, discontented with the civil war, wishing to restore unity of Mexico, overthrew President Zuloaga and offered the presidency to General Miramon. The latter reached the capital on January 24th only to put down the coup and restore Zuloaga. Now discredited, the President became a puppet of his 'restorer'.
General Miguel Miramon
El Tigre de Tacubaya _ 1859
While 1859 began, Miramon seemed to be about to obtain a complete victory. On February 16th, he left Tampico to besiege Monterrey. But, a month later, while he was about to begin the siege, he was forced to return to Mexico City which was under attack.
Indeed, instead of attacking Guadalajara, General Degollado bypassed it, took Guanajato on March 3rd and marched upon the mexican capital with his 6.000 men. In the city proper, the 4.000 soldiers of the garrison under General Corona entrenched themselves, waiting announced reinforcements. Degollado arrived on March 22nd and occupied Tacubaya and Chapultepec but delayed the main attack. On April 2nd, when assaults were ordered at Tlaxpana and San Cosme, they were repulsed.
On April 10th, the relief army under General Marquez finally arrived near Tacubaya, and the following day, routed the Constitutionalists. Marquez won then the dark nickname of 'Tigre de Tacubaya' after ordering the execution of all its prisonners, soldier as civils [5].
General Leonardo Marquez
Until autumn, no great fights occured.
Miramon defeated the reconstitued army of General Degollado at the battle of Estancia de Vacas on November 13th then defeated generals Ortega and Rocha in Jalisco and Colima during December.
Leyes de Reforma
On April 6th, Juarez won a diplomatic victory with the recognition by Buchanan's administration of the legitimacy of the Constitutionalists. In turn, the Conservatives got closer of european powers, signing a treaty with Spain. Juarez also signed a treaty with the USA, exchanging trade concessions for arms supply, but despite of Buchanan's will, it was never ratified by the Senate.
To fund the war, Juarez also issued the 'Reform Laws', decreeing nationalization of Church's properties.

Southern Campaigns _ 1858-1860
Southern Mexico didn't see major actions until the end of war, excepted when the Conservatives, under General Negrete, repulsed an attack of Villahermosa in October 1858 and, under General Cobos, took Oaxaca a year later.
In May and June 1860, Conservatives, under General Marin, invaded and took control of Yucatan.
Chiapas was only invaded in early autumn but was never really pacified until 1865.
To Tijuana ! _ 1860-1861
The final act of the civil war began on February 17th, when General Miramon and 9.000 men left Tampico, again, towards Monterrey. This time, there was no attack on Mexico City by Degollado to prevent him to besiege. Despite guerrilla, the siege was begun on March 19th, just four days after Juarez and his ministers left it for Chihuahua.
At the battle of Saltillo on March 27th, the Constitutionalists under General Ortega failed to relieve the siege. Monterrey surrendered a week later.
Juarez arrived in Tijuana on July 10th, still fleeing the seemingly unstoppable advance of Miramon.
The crossing of the Colorado only took place on November 20th because of difficulties to secure supply lines in a region plagued by constitutionalist guerilleros.
The Lower California Campaign then begun.
Juarez attempted to get american help but in America were coming the clouds of a war.
Tijuana fell on March 1st.
OTL Map
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It's hard to find information about this civil war. This chapter is essentially based on the informations of antorcha.net. However, I've recently acquired a reedition of a book written for Diaz in early 20th century; but, my mastery of Spanish being not very perfect, it will take some time to deliver a corrected version of this update.
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[1]: Our POD. IOTL, Vera Cruz declared first its support for the Plan de Tacubaya, but its governor was convinced by General Ignacio de La Llave to come back on his decision.
[2]: As IOTL.
[3]: Instead of Vera Cruz IOTL.
[4]: ITTL, the Constitutionalists intercepted battle plans of the Conservatives and won.
[5]: As IOTL