Complex sentence: Epaminondas also asked another 11.000 soldiers from Fidelios, who was completing the Siege of Tarija at the time and who wholeheartedly accepted his ally's pleading and by using forced march those men joined the Argentinian army in the late afternoon of the same day.
Split into simpler sentences: Epaminondas also asked another 11.000 soldiers from Fidelios, who was completing the Siege of Tarija at the time. The latter, wholeheartedly accepted his ally's pleading and by using forced marches he had those soldiers delived to the Argentinian army in the late afternoon of the same day.