But first a short stab at some philosophical definitions and contextualisation on my part:
Descartes had done some work which led to the conclusion that he existed and so did God (for a few reasons) but had come to the conclusion that there was what has been characterised as a Mind Body Split.
1** Neither Leibniz or Spinoza were happy with this..
2** Spinoza postulated that in fact there wasn't a split and that it was all God (or nature).
3** Leibniz came to the conclusion that everything was ultimately reducible to 'monads' which weren't physical.
Back to the history..
Unlike many historic figures working in the same academic niché at the same time Spinoza and Leibniz actually met in November 1676 when Leibniz, traveled to The Hague to visit Spinoza, if I'm correct (and it's not a hoax) there's even some correspondence between the two of them here.
Baruch (Latinized to Benedict) de Spinoza (1632- 1677) was the son of Portuguese Jews he was born and brought up in Holland and suffered the excommunication from his faith on July 27, 1656, he died at the age of 44 as a result it is thought of industrial factors around his day job of grinding lenses.
Some label him as an atheist or perhaps a Pantheist, one of the catch phrases that was attributed to him was Nature Abhors a vacuum But it seems that Heracles came up with it first.
Gottfried Wilhelm Leibniz (July 1, 1646 – November 14, 1716) As mentioned before Gottfried held to the concept of everything being reducible to Monads. (here's more about Monads).
Leibniz was a bit of a prodigy who studied Aristotle at a young age, he lost his father when he was six, he was a Lutheran.
Among the things that Leibniz left us with was that " we live in the best of all possible worlds."
Both of these gentlemen were also mathematicians but Leibniz (German) was the superior in the field of Maths who independently of Newton discoveredinfinitesimal calculus.
As the course leader (Citylit Philosophy) Scott pointed out today Spinoza and Leibniz shared many assumptions and used the same source/s for their work (principally Descartes) what they arrived at though were two quite distinct conclusions and in fact Leibniz was critical of Spinoza's philosophy (perhaps because he had more of an ego than the self effacing Spinoza?)