"...necessity of victory before winter fell in Chile's frigid south. The rapid collapse of Surista positions since the fall of Los Angeles in the early spring had helped, however, and the overwhelming advantage in light artillery and aerial firepower finally tipped the scale; Alessandri was warned by Altamirano that a siege of Puerto Montt, even with the Suristas severely limited, would be an ugly affair, likely lasting weeks and with the enemy fighting to the last man.
It was indeed worse than that; after the rapid advance from October to December through southern Chile inspiring government forces (particularly after their seizure of Valdivia on Christmas Day), fighting got bogged down in the teeth of resistance in the most dedicated of Surista territory, the country of itinerant preachers, several churches per town, and deep superstitions that blended pre-Christian beliefs with the most dogmatic Catholicism anywhere in the Southern Cone. The terrain west and south of Valdivia lent itself to difficult fighting even at the head of summer, but by late January the Army was moving, its supply lines even longer than before but supported by resources through Valdivia by sea, on towards Puerto Montt, clearing every town house by house. This was the ugliest stage of the Civil War; Bartolome Blanche, later a major figure in the Socialist Republic's "Red Juntas," [1], described in his diaries as a brigade commander in those hard months what can charitably be described as scorched earth campaigning, less charitably as gruesome war crimes. Towns were burned to the ground as crops and livestock were confiscated; on at least three occasions on the road to Puerto Montt, Blanche witnessed but did nothing to interrupt cases where women and children were ushered into churches that were subsequently burned to the ground, after witnessing all the men and boys over the age of twelve killed in the town square, bludgeoned or bayoneted to save bullets and powder.
Puerto Montt's landside defenses were finally invested in early February, after which followed not a few weeks of siege but rather over three months, with the city not falling until May 20. Aldunate pointedly refused entreaties to evacuate his men by sea - "evacuate where?" he asked incredulously - and surrender for many Suristas was not an option, so convinced were they that they were fighting a holy war against a barbaric, godless enemy. Planes bombarded the city every day with dynamite and other crude mining explosives, or strafed defensive trenches, but nonetheless the Suristas held on doggedly against the Colorado forces. Altamirano, after two failed offensives in mid-March had failed to breach the trenches, instead elected to starve the city's defenders and civilians out, focusing huge attention on destroying the city's docks to make it impossible to bring food ashore from the fishing villages dotting the fjords of southern Chile and sinking vessels that passed into the Seno de Reloncavi, after capturing high ground near Colaco that gave his planes total domination over the Chacao Channel and Sea of Chiloe. Inside the city, public order began to rapidly deteriorate as salted fish ran out and whatever meat was left was prioritized for defenders; by late May, people were eating shoe leather, mice, and dirt to stay full, and when the city eventually collapsed of hunger, it was an exhausted, grim populace who were surrendering to Altamirano, not dogged resistance fighters.
How violent the fall of Puerto Montt actually was is debatable in Chile even today; Patria y Libertad commanders made it an article of faith for decades that thousands were slaughtered wholesale, including crucifixions and beheadings. This is highly doubtful, and not just considering the source; even Blanche, who kept meticulous records of his colleagues' depravity in the south of Chile, described Puerto Montt's collapse as remarkably civilized compared to some of what he had seen just months earlier. The besiegers were decently fed and by May had become very comfortable lobbing artillery and dropping bombs rather than attacking, and there was little frustration to take out; Surista leaders like Silvestre Ochagavia and Francisco Valdes, when captured, were quickly condemned and executed by firing squad on the beaches of the Seno de Reloncavi in proceedings best described as extrajudicial, but soldiers by all accounts were given the first bread and dried meat they'd tasted in weeks. Narratives, it turn out, are much more powerful to a conquered people than the truth.
The Civil War effectively ended May 20-21st at Puerto Montt, in no small part because Aldunate, in the end, did evacuate - in a small dinghy under cover of night, then by packmule over the Andes as winter started to set in and thereafter smuggled in a barrel from Chubut to Brazil, and from then on to Havana, where he lived in destitution for several years until he began receiving a generous, anonymous stipend to live more comfortably in a second-story apartment a few blocks off the city's famed Prado. His presence was quiet, only occasionally joining other right-wing Chilean exiles for dinner; upon the imposition of the Socialist Republic in 1924, his company in Cuba became much more liberal in flavor, though he often shunned men whom he knew to have been Alessandrists. He commented seldom on Chilean politics publicly or in published writing, but he did compile extensive diaries and memoirs that were published posthumously following his death of stroke in 1931. A rallying figure for the Chilean far-right, he was not; but an important figure in Chilean postwar history, he was, as his hour ended in the south in 1918.
The defeat at Puerto Montt meant that, with the exception of scattered guerilla bands in the southern Andes and on Chiloe Island, the war was over, and the soldiers could begin to return home. Alessandri was ecstatic - his Radical Republic had, at last, triumphed over a dogged enemy that at the outset of the war had enjoyed considerable public support, especially in the rural south. The program to reintegrate the whole of the country was still to come - schools built, churches repaired, roads paved - but first there was a time to take a deep breath and rejoice, because as Chile had discovered repeatedly since its fateful decision to dispatch ships to Chimbote Bay in September 1913, one never knew how long such relaxed breaths would last..."
- Between Two Chiles
[1] If you're reading between the lines and deciphering that between Grove and Blanche the Socialist Republic will have a very military flavor, you're correct.