This is only true in some of the many wars he engaged in. I'll break it down in chronological order, and give a brief summary of the cause/s of each war, as well as who was ultimately responsible, starting from the War of the Third Coalition, since that was the first conflict that France engaged in when Napoleon was in power (not including the War of the Second Coalition, since that was not started when Napoleon was in power).

War of the Third Coalition (1803-5): This "war" was actually two different wars that broke out in the span of a year and a half, both of them against France. The first was when Britain declared war on France in 1803. The reasons given were Napoleon's repeated violations of the terms of the Peace of Amiens (1802), whereby he promised to remove French troops from various regions but failed to do so. The British had also failed to remove their own troops from Malta. Both sides had violated the peace terms in various ways, but it was the British that escalated the situation to war. The second "war" involved in this conflict was when the Austrian and Russian empires, as well as some other minor powers like Sweden and Naples, formed a broad coalition against France in 1804-5. There were a variety of reasons, again, such as Napoleon declaring himself the "King of Italy", a title that the Habsburgs of Austria traditionally held, as well as his unlawful arrest and execution - without a trial - of the Duke d'Enghein, a prominent nobleman that Napoleon suspected of plotting against him. This outraged the aristocratic regimes across Europe. However, despite many provocations from Napoleon, this second war was again started by the Allies.

War of the Fourth Coalition (1806-7): This war - which some historians view as merely a continuation of the War of the Third Coalition - was started by Prussia, the primary belligerent of this specific conflict. King Frederick William III was pressured by his wife, Queen Louise, and the pro-war elements of his council to declare war on France. They feared French encroachment in Germany, following the crushing defeat of Austria in the War of the Third Coalition, and the subsequent dissolution of the Holy Roman Empire and establishment of the Confederation of the Rhine, a French satellite state in western Germany. The Prussians formed an alliance with the Russians, who were still fighting Napoleon despite retreating east following their defeat at Austerlitz (1805). Thus, this war wasn't really a new one, just a continuation of the Third Coalition war, with one belligerent gone (Austria) and another taking its place (Prussia). Despite the Prussians being the ones to declare war on France - something Napoleon did not expect in the slightest - they were defeated and their entire country conquered in only a couple of weeks.

Invasion of Portugal (1807): This was Napoleon's first unambiguously aggressive war. He was angry at Portugal's refusal to adhere to his new Continental System, a Europe-wide trade embargo against Britain. Portugal's economy was heavily dependent on British trade, and so it would have been economic suicide to follow Napoleon's policy. Napoleon, with the aid of his ally Spain, invaded Portugal and partitioned the country between them. The Portuguese royal family fled to their colony in Brazil.

Invasion of Spain (1808): Another of Napoleon's aggressive wars. He personally despised the King of Spain and his family, viewing them as incompetent, untrustworthy and pathetic. He did not want to have to rely on them for anything, and wanted a regime change. He decided his brother Joseph (who was currently the King of Naples, having been placed there by Napoleon) would make for a better and more compliant king, and so he had the Spanish royal family arrested, and his brother put on the throne. Before he did this, however, he garrisoned tens of thousands of French soldiers across Spain, to act as "protection", he claimed, but as soon as he arrested the royal family he gave them orders to capture the towns and cities they were in. The remnants of the Spanish government offered resistance, which was shortly followed by British reinforcements, thus beginning the six-year-long Peninsula War.

War of the Fifth Coalition (1809): This was started when the Austrian Empire, without any allies of its own, declared war on France in April of 1809. They - along with everyone else in Europe - had been horrified by Napoleon's actions in Portugal and Spain, and there were widespread fears that Napoleon was planning on overthrowing the Habsburgs and putting a relative on the Austrian throne next. They also wanted revenge for their several defeats in the past at the hands of the French (1796, 1801, 1805) and were intent on reclaiming lost territory and cutting down French power. They began the war by invading the Kingdom of Bavaria, an ally of France's. Napoleon did not want this war - already having deployed 200,000 of his best troops in Spain and Portugal - and spent months trying to dissuade the Austrians from embarking on it, albeit unsuccessfully. At this point they didn't believe a word of what Napoleon said, since his reputation and honour was in the gutter at this point following his actions in Iberia.

Invasion of Russia (1812): The alliance that Napoleon had forced upon the Russians at the Tilsit peace talks in 1807 had broken down by this point, as both sides repeatedly violated the terms of the treaties signed - Napoleon by annexing land in north-western Germany, and Russia by annexing land along the Danube. The Russian economy was severely damaged due to being forced to adhere to the Continental System - like Portugal, Russia's economy depended on British trade - and there was widespread discontent among the nobility due to Russia being seen as subordinate to France. Finally, the Russians were uneasy about the establishment of the Duchy of Warsaw, a Polish client state that Napoleon created out of land seized from the Austrians, Prussians and Russians and returned to the Poles. The Russians feared this would lead to revolts in their Polish provinces. It was all of these factors that led to war seeming inevitable in 1812. Though the Russians provoked the French by stationing thousands of troops on the border with the Duchy of Warsaw, it was Napoleon that struck first, crossing the Neiman River and invading Russia with an army of 700,000 - the largest in history until World War I.

War of the Sixth Coalition (1813-14): Following Napoleon's defeat in Russia and the destruction of almost his entire army, his many old enemies were encouraged to resume the struggle against French hegemony. As the French retreated back to Germany and the Russian armies stormed across Eastern Europe, Prussia rose against the French, threw out the French garrisons, allied with Russia and declared war on France. After much hesitation, the Austrians also joined. This new "coalition war" was technically started by Prussia and Austria, in that they were the ones that declared war on France, but the major conflict had already been started by the French the year before, and these new belligerents merely joined in later. Neither country would have dared declare war on France if the invasion of Russia hadn't been such a disaster. And at this point Prussia was basically an occupied country, and the Prussians saw their war not as an aggressive war but as a war of liberation (which I believe it's actually called in some places in Germany).

War of the Seventh Coalition (1815): This was started by the Allies following Napoleon's return to power. Napoleon sent letters out to all the courts of Europe promising to not engage in any wars and to limit himself to France's current borders, but at this point it was too little and too late. Nobody trusted or respected him, and it was universally agreed that there could be no peace or stability in Europe with him in power. Every major Allied country swore an oath not to lay down their arms until Napoleon was defeated and overthrown again.

To summarise:

War of the Third Coalition: Defensive war

War of the Fourth Coalition: Defensive war

Invasion of Portugal: Aggressive war

Invasion of Spain: Aggressive war

War of the Fifth Coalition: Defensive war

Invasion of Russia: Aggressive war

War of the Sixth Coalition: Defensive war

War of the Seventh Coalition: Defensive war

It's important to keep in mind that in every conflict except arguably the invasions of Portugal and Spain, both sides had provoked the other in various ways, and broken many treaty agreements. There were no good guys or bad guys in this conflict, and both sides had valid reasons for doing what they did in many cases (except the aforementioned invasions of Portugal and Spain, which were disgraceful and had no acceptable justification).