The Shadows of Elisa Lynch, by Siân Rees<br></br> The Empress of South America, by Nigel Cawthorne

A vicious adventuress has inspired two biographies and a novel. Jean McNeil on the Irish Evita

Finally, proof the Zeitgeist really does exist. What else are we to make of the virtually simultaneous publication of two history-biography hybrids and one novel which share as the subject of an obscure woman, a reclusive country, and a war hardly anyone (in Europe, at least) has so far heard of?

Siân Rees and Nigel Cawthorne's books both trace the duly shadowy outlines of the life of Eliza Lynch, an Irishwoman who was, we are told in the latter's somewhat salivating subtitle, briefly the richest woman in the world. The source of her riches was Paraguay, the Poland of South America, a landlocked country sporadically fought over by neighouring titans Brazil and Argentina, and plundered by a succession of sociopaths ending in the longest dictatorial regime in South America (Alfredo Stroessner, from 1954-1989). To this biographical fiesta we could add Anne Enright's lushly imagined novel, The Pleasure of Eliza Lynch, (Cape), a "faction" based on a life burdened by more interpretation than fact.

Indeed, the facts are few, and even these are in dispute, as Eliza was known to be less than truthful about them. Born in County Cork in 1835, her family fled the Irish famine and fetched up in the turbulent Paris of the Second Republic. In Paris, she promoted herself as a language teacher to courtiers and stray foreign oligarchs. On the way, her biographers concur, she had been married at 15 to a Frenchman, lived in Algeria, and eloped back to Paris with a Russian.

She was only 19 when, in 1854, she met Francisco Solano López, the eldest son of the self-declared El Supremo of Paraguay and his heir apparent. They had, it seems, instant and permanent sexual chemistry. Eliza sailed to Paraguay, bore López five children (although he never married her) and was widely considered to have encouraged him into the War of Triple Alliance (1864-70) in which Paraguay lost most of its male population and a chunk of its national territory to Brazil, Argentina and Uruguay.

Where the facts end and interpretation begins, the biographers circle each other. What has been discarded by one is picked up by the other. Cawthorne sets the political scene, tracing the origins of López's terrifying tropical dystopia, while Rees writes knowledgeably about the post-Napoleonic Paris Eliza abandoned to seek her fortune in mysterious Paraguay. Cawthorne's is the blunter pen: by page seven we know López as "the biggest mass murderer since Genghis Khan" and that Eliza "bled the country dry". A certain general is "bloodthirsty", and Francisco's mother "lorded it over her subjects". Thus he chomps through his personnel, erring on the pantomime-villain side of characterisation. That his style is effective and engaging despite bouquets of cliché is due to the delight he takes in the ironies of fate, even if he seems hungry for Eliza's demise.

The Shadows of Elisa Lynch is subtly written, stocked with vivid descriptions of wildlife and landscape and arresting phrases (a day in the war is "atrociously beautiful"). Rees is a determined researcher, consulting primary sources in Spanish and French, and she conveys the subtleties of 19th-century diplomacy and South American politics, such as they were.

Crucially, she displays more sympathy for her subject. "If her spirit had not already been broken by the unremitting successions of blows dealt her over the past years, surely it admitted defeat during her first days in Europe," she writes, of a woman who has, 12 pages earlier and in the middle of the abominable suffering of her compatriots, schemed to buy war-abandoned lands the size of Belgium and Holland combined.

Both writers whirl the same carousel of personality: Eliza the military risk-taker, the dab hand at the property market, the fashionista of her day, the linguist who knew how to bear a grudge, but even so she remains something of a cipher. This is where fiction steps in, in the form of Anne Enright's novel, written from both Eliza's perspective and that of her Scottish doctor. Enright's fictional Eliza meditates on her pregnant state and understands she has become "evil". But after reading the biographies it's hard to believe Eliza was capable of lush subjectivity, that she was anything other than a utilitarian individual, inhabiting an interior desert of bare acts.

The carnivalesque and sickening brutality that each author takes pains to draw, although in a different colour scheme, would seem to demand an examination of the psychopathy of absolute power: of the conditions in which unscrupulous people become dangerous, when corrupt natures begin to luxuriate in carnage. But neither writer judges their subject. This is important, because it is one of the reasons why we read historical biography: to re-question the values we have assigned to history, and to pass judgement on how individuals conduct its disasters, as well as not to repeat its mistakes of, say, being led into unwinnable conflicts forged in the name of patriotism which are really about the enrichment of a small coterie. Nor do the books trace the Eliza effect on modern Paraguay, a kleptocracy whose current president is facing possible impeachment over, among other things, alleged possession of a stolen car. Could this be because we are only interested in neglected countries insofar as they cross with the stories of the British subjects who become briefly intertwined in them?

In the end, their war speaks as much about Lynch and López as any comment on the disaster of personality. Both Cawthorne and Rees give over half their books to unsparing accounts of the Paraguayan killing fields, nauseatingly gripping with their depictions of torture methods – the skinned flogees and raped women, the peasants thrown at the enemy "like sandbags". We end with a ripe understanding of the calamity of this, and perhaps all, wars: completely futile hells spawned in the vortex of political ambition.

Jean McNeil's novel 'Private View' is published by Weidenfeld